Whoever stands in prayer during Ramadan out of faith and seeking reward, his previous and subsequent sins will be forgiven.

The Shaykh : Among its special features is also that whoever stands in prayer during it out of faith and seeking reward, Allah will forgive him his previous and subsequent sins. And among the standing in prayer during Ramadan is the Tarawih prayer that we are praying now at the beginning of the night. It is part of the standing in prayer during Ramadan. It is called Tarawih because the righteous predecessors (may Allah be pleased with them) used to lengthen it greatly, meaning they used to lengthen it considerably. So when they prayed four rak'ahs, they would rest, then resume the prayer. And when they prayed four, they would rest, then resume the Witr with three. Therefore, it is called Tarawih, derived from where? From rest, from rest. So if a person says, "We do not find that we stand the whole night or most of it, so how can it be true that we have stood in prayer during Ramadan?" The answer is: It is a glad tidings from the most truthful of people in speech, and he is the Messenger of Allah (peace and blessings be upon him). He stood in prayer with his companions until the middle of the night, and they said: meaning, if you had lengthened it further to the end of the night, he said: Even if he is sleeping on his bed, and he stood with the imam until he concludes, then Allah the Exalted writes for him the standing of a night, a complete night. And this is glad tidings for the believers, and it indicates that it is obligatory for a person to maintain the Tarawih prayer with the imam and not to be a wanderer who prays two or four rak'ahs in this mosque, then prays in another mosque, then in a third, so his time is wasted and his reward is wasted, because the standing of the night is not written for you except if what? Except if you remain with the imam until he concludes. And here a questioner might ask and say: If the mosque has two imams, one of whom prays half of the standing and the second prays the remaining half, and the first concludes, then if you conclude with the conclusion of the first, is the standing of a night written for you?
The answer is no, the standing of a night is not written for you, because the second imam is a deputy for the first, completing his prayer. And the evidence for that is that the second is the one who prays the Witr, and this indicates that what the second prayed is the remainder of what the first prayed. So if you want the standing of the night to be written for you, wait until the second imam finishes the prayer, then conclude with the conclusion of the second.