A Person joined the prayer while the imam is in recitation but as soon he made the starting takbeer of ihram the imam made ruko.
Should the person complete reciting the Fatiha or should be bow immediately?
He should bow because : “The imam is made to be followed. Bow when bows,rise when he rises…””Prostrate when he prostrates” (wordings of hadith of Aisha and Anas radhiallahu anhuma in Bukhari)
Except in the case when you feel you can finish your recitation of the Fatiha before he rises from the rukoo then there is no issue in doing this but it is better that you bow with him and you will be get the rakah even if you were not able to recite the Fatiha or complete it in this case.
Shaykh Abu Bilal Al Hadhrami hafidhahullah
Abu Muhammad Nezam Al-Hindi