1751/1 - Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah’s peace and blessings be upon him) said: “Is he who raises his head before the Imam not afraid that Allah may transform his head into that of a donkey or his shape into that of a donkey?” [Narrated by Al-Bukhāri and Muslim]
1) It is prohibited to move ahead of the Imam in prayer, given the warning issued in this respect. A person led in prayer should follow the Imam and do any move right after him.
2) The Prophet’s statement that a person who does so may transform into the shape of a donkey indicates the enormity of this act.
There are four conditions for a person led in prayer in relation to the Imam:
1) He acts and moves ahead of the Imam. This is prohibited, in light of the stern warning reported in this regard.
2) He lags behind the Imam. If this is due to a valid excuse, there is nothing wrong with it. But if he does so without an excuse, his prayer becomes invalid if the delay occurs in one of the pillars of prayer; this is not permissible just like moving ahead of the Imam.
3) He acts and moves along with the Imam, which is disliked.
4) He acts and moves right after the Imam, not along with, ahead of, or well after him. This is the Sunnah and the Prophet’s guidance that should be observed.