The Questioner says: Due to the spread of the corona virus; some precautionary measures have been introduced by governments of various countries, such as:
1. Washing the hands with alcohol-based sanitisers in order to kill microbes. What is the ruling of using them, especially as they are highly recommended by medical experts?
Alcohol, as you are well aware is an intoxicating substance. It is the essence of present-day wine, so there is hardly a (type of) wine (available) from a winery except that its origin, basis and foundation is alcoholic, as they (i.e. the experts) mention. So upon this; alcohol is haraam. It cannot be consumed because it is an intoxicant.
What remains is: can it be used for other than consumption or not?
Evidently, if it is alcoholic; then the Prophet ﷺ mentioned eight ways in which it cannot be used and did not limit this solely to drinking.
[1. لَعَنَ اللَّهُ الْخَمْرَ وَشَارِبَهَا
Allah has cursed wine and its drinker
And its server
And its buyer
And its seller
And its presser
And the one for whom it is pressed
And its carrier
8. وَالْمَحْمُولَةَ إِلَيْه]
And the one for whom it is carried.] (1)
So this individual is considered to be using this alcohol on his hands, even if he is going to remove it.
According to a number of scholars alcohol is impure. There is no doubt that there is a consensus that it is impure, however, they differed regarding (the nature of) its impurity; is it’s impurity tangible or intangible?
The majority of scholars view its impurity to be tangible. If its impurity is indeed tangible than it is not permissible to use it. Not by applying it to the hands, body, clothing or anywhere else for that matter; because it is (tangibly) impure.
《 إِنَّمَا ٱلْخَمْرُ وَٱلْمَيْسِرُ وَٱلْأَنصَابُ وَٱلْأَزْلَٰمُ رِجْسٌ 》
Indeed, wine, intoxicants, gambling, [sacrificing on] stone alters [to other than Allah ], and arrows for seeking luck or decision are impure.
The term ‘rejas’ has been explained with the meaning ‘impure’.
《مِّنْ عَمَلِ ٱلشَّيْطَٰنِ فَٱجْتَنِبُوهُ 》
from the work of Satan; so avoid it.
Do not drink it or apply it to your hands – avoid it. Whether it is for drinking, washing, cleaning or anything else that it can possibly be used for; because it is impure.
His statement ﷻ
Suggests that it cannot be used in any means at all because Allah ordered for it to be avoided and to stay away from it and washing (the hands) with this alcohol means not avoiding it.
What is apparent is that if it is confirmed that this alcohol is from that which intoxicates – which it is – then we advise with refrainment from it.
It is due to this that a number of our scholars of recent times view alcohol contained perfume to be haraam and impermissible to use; because this intoxicating alcoholic substance has been mixed with it.
In this case the user falls under the (cursed) column of carriers of alcohol; on his clothing and body when he applies this alcohol contained perfume – providing it has not been transformed or completely eradicated by other substances whereby there remains no presence or trace of it whatsoever, this is an entirely different matter.
For indeed the scholars permit (the usage of) something haraam once it has been transformed because there is no longer a trace of it nor does it exist due to this transformation. As for if it still exists in some form, then its use is impermissible.
This alcohol which is being used to clean the hands and that the medical experts are advising with; we advise to refrain from it; regardless of whether we say that the impurity of alcohol is a tangible impurity – in which case it must be left without question – or an intangible impurity; in which case it is appropriate for it to be left because Allah says:
So we stay away from it and use alternative substances and sanitisers. This is the safest option.
But if the matter is actually how these medical experts are saying; that the microbes cannot be removed except by the likes of this substance alone; then Allah ﷻ says:
《قَدْ فَصَّلَ لَكُم مَّا حَرَّمَ عَلَيْكُمْ إِلَّا مَا ٱضْطُرِرْتُمْ إِلَيْهِۗ 》
and He has explained in detail to you what He has forbidden you, excluding that to which you are compelled.
So you are not at fault, by the permission of Allah because this is a state of necessity, which is a different matter. So if this affliction will be removed through the the usage of the likes of this substance; then there is no problem with this, in sha Allah – and Allah is most knowledgeable.
It is due to this that Shayk Al-Islam (may Allah have mercy upon him) – as mentioned by some of the scholars; viewed the eating of pork to be something indisputably haraam, but as for it coming into contact with the body for a need, such as medicine or something of this nature; then he states there to be no problem with this due to a necessity, all the while eating it is not permissible.
This applies even more so to this substance thats (impurity) is disputed. So if there is a need to use it – not for drinking, for indeed drinking it is haraam in every case, whether it is drank as medicine or not – rather this need is only for washing the hands, and there is no alternative substance except this, then this is a different matter.
The default is that it is not permissible, haraam. However in the event of necessity, if an alternative to this substance is found then it cannot be overlooked. But if there is no alternative, then Shayk Al-Islam viewed applying gellatin to oneself in the event of an emergency not to fall under the same ruling as eating it, so in the event of an emergency it is OK.
Having said that; it is appropriate for the muslim to keep away from using this alcohol to wash his hands (unless there is no alternative).
Thus, we advise the muslims to seek alternative medicines to these haraam medications. The default regarding the usage of alcohol is that it is forbidden for both drinking and cleaning except in the case of necessity, excluding drinking.
As for drinking it; this not permissible, even as part of medical treatment:
[إنَّ اللَّهَ لَمْ يَجْعَلْ شِفَاءَ أُمَّتِي فِيمَا حَرَّمَ عَلَيْهَا]
Verily Allah has not placed any cure for my nation within what he has forbidden upon it.
In addition to this: Is to avoid greeting with handshakes and embraces. (Instead) they advise to greet by waving, similar to the greeting of non-muslims. What is the ruling of stopping handshakes in this case ?
If something of this nature has occurred and there are some known instances in which it was passed on by way of handshaking or embracing; then it is appropriate for the people to avoid handshaking and embracing.
(Avoiding) the harm of a danger takes precedence over fulfilling a good deed.
So this is to be left preventatively so that one does not catch this illness from someone that has it.
The Prophet ﷺ said:
[” لاَ يُورِدُ مُمْرِضٌ عَلَى مُصِحٍّ ”]
A sick person should not be put before a healthy person. 
This applies even to handshaking; that you should not shake his hand.
He ﷺ also said:
[“إِنَّا قَدْ بَايَعْنَاكَ فَارْجِعْ ”]
We have certainly accepted your pledge of allegiance, so you may return. 
He ﷺ usually accepted pledges of allegiance by shaking hands, but stopped so nothing of that nature could occur .
So, if it is known that this harmful illness is passed on by way of handshaking and embracing; in this case there is nothing wrong (with stopping).
But if this is not the case at all, and it is all just guesswork, assumptions, inclinations and inaccurate research; then this is does not apply so do not pay them any attention.
The suspension of public gatherings and circles of knowledge. We have seen that some of some the scholars have implemented this order. Do we have to refrain from public gatherings until Allah removes this affliction from the country?
If the country in which you are settled or residing has outlawed this; refrain.
If the country has banned this with (the support of) its scholars; we advise you not to oppose the rulers. Opposition to them is unacceptable especially in the likes of these matters in which they have reached a conclusion based upon their own understanding. Be patient and Allah will create an opening as well as a way out.
We give the benefit of the doubt to our rulers (i.e. Muslim rulers) especially those (i.e. of Saudi Arabia) particularly when their view coincides with the view of their scholars.
So do not oppose them by going around and setting up circles of knowledge in masaajid whilst they have prohibited this. Do not oppose them, remain in your home and if holding circles of knowledge at home is not under scrutiny, then this is a separate matter.
As for openly opposing the rulers; we do not advise with this.
[ كُلُّ أُمَّتِي مُعَافًى إِلَّاالْمُجَاهِرِينَ ]
My entire ummah will be pardoned (for their sins) except those who do them openly. 
Answered by :
Shaykh Abu Bilal Al Hadhrami hafidhahullah
Answered on :
25th Rajab 1441
20th March 2020
Translated by :
Saami ibn Daniel Al-Ghaani
 Narrated by Ibn Umar (may Allah be pleased with him) in Abu Dawud (3674)
 Recorded in the saheeh of Ibn Hibaan
 Narrated by Abu Salamah ibn ‘Abdur Rahman ibn ‘Awf (may Allah be pleased with him) in Muslim (2221)
 Narrated by Sharin ibn Suwade AlThaqafee (may Allah be pleased with him) in Muslim (2231)
 i.e. the passing on of leprosy. Sharin ibn Suwade AlThaqafee reported that there was a man in the delegation with leprosy, so the Prophet ﷺ sent this message to him (instead of shaking their hands). This is mentioned in the same hadith cited above.
 Narrated by Abu Hurriera (may Allah be pleased with him) in AlBukhari (6069) and Muslim (2990)