Raising from rukoo' or sujood before the imaam
16-1-2016 | IslamWeb
Question:
This is a bit urgent, does doing raising from rukoo' or sujood before the imam invalidate one's prayer? If so under what conditions (intentional/unintentional) does the prayer need to be repeated?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad 
is His slave and Messenger.
If what you mean is that the person led in prayer raises from rukoo’ (bowing) or sujood (prostrating) before the imaam, then the answer is that it is not permissible for the person led in prayer to do so deliberately or to precede the imaam in any actions of the prayer because it is an obligation to follow the imaam in all the pillars of the prayer and there is a stern warning in regard to the one who does that intentionally, as confirmed in a hadeeth from the Prophet . Abu Hurayrah 
narrated that the Prophet said, “Does one of you not fear that if he raises his head before the imaam, Allaah will turn his head into the head of a donkey.” [Muslim]
There is a difference of opinion about the validity of the prayer of the person led in prayer if he does so deliberately. Shaykh Ibn Taymiyyah 
said:
“Preceding the imaam is forbidden according to the consensus of all the leading scholars. No one is allowed to make rukoo’ before the imaam or to raise before him or to make sujood before him. Indeed, there are many ahaadeeth of the Prophet about the prohibition of doing so… however, if he precedes the imam out of forgetfulness, then his prayer is not invalidated. Nevertheless, he should delay following the imam to the extent that he preceded him... However, if he deliberately precedes the imam, then there are two known opinions about the invalidity of his prayers in the School of Ahmad and others.”
The view that we adopt here at Islamweb is that his prayer is not invalidated, and therefore, the person led in prayer is not obliged to repeat the prayer in which he preceded the imam in bowing down or prostrating and the like, but he is sinful in case he does so deliberately.
As regards the case of forgetfulness, then he is not sinful and his prayer does not become invalid, but he should return to following his imaam.
The Fiqh Encyclopedia reads, “If the person led in prayer raises his head from rukoo’ or sujood before the imaam, then he should return to his position and this is not considered as two rukoo’s or two sujoods according to the agreement of all the scholars.”
For more benefit, please refer to fatwa 85130.
Allaah knows best.