The questioner says:
An Imām of a Masjid prays the audible prayers whilst reading directly from a Mushaf, the majority of his situation is like this, so what’s the ruling on prayer behind him?
The prayer is valid, however this Imām we say to him if he hasn’t memorised, then he should appoint others from those who have memorised to lead the people in prayer, and if it’s a must (he still leads) then he should recite from what he has memorised, Allah doesn’t burden a soul beyond its scope.
This action of holding the Mushaf was not done by the Prophet ﷺ, nor was it done by the companions – May Allah be pleased with them – at the time of the Prophet ﷺ, the most whats been reported was concerning Aisha that when standing at night she would get a servant of hers to lead prayer and they would recite from the Mushaf.
And whomsoever insists of this action, will leave off (i.e lose out on) memorising the Quran, turning to it, revising it etc.
Shaykh Abu Hamza Hassan bin Muhammed Ba Shu’ayb – may Allah preserve him
Abu Mālik Nāsir Al-Ma’mary