Hazrat Ali (may Allah be pleased with him) bin Shiban narrates that we came to the service of the Holy Prophet (peace and blessings be upon him) as a delegation. We pledged allegiance at his blessed hand and performed prayer behind him. The Holy Prophet (peace and blessings be upon him) saw a man praying alone behind the row, so he stood by him. When the man finished his prayer, the Prophet said, "Repeat the prayer, for the one who prayed alone behind the row, his prayer is not valid."

Ibrahim says that he will repeat the prayer.

Hazrat Ata says: Do not stand alone.

Hazrat Wabisah bin Ma’bad narrates that a man offered prayer alone behind the rows, so the Holy Prophet (peace and blessings be upon him) ordered him to repeat the prayer.

Hazrat Dahhak narrates that Hazrat Hudhaifah (may Allah be pleased with him) was asked about a person who performs prayer alone behind the rows. He replied that he will not repeat the prayer.

Hasan says that his prayer will be valid.

Hasan, regarding the person who enters the mosque but does not have the strength to join the row, says that if he prays behind, his prayer will be valid.

Hasan was asked: If a man misses one rak‘ah, joins the prayer, then the imam’s wudu’ breaks, so the imam takes the hand of this follower and puts him forward, what should he do? Hasan replied: He should pray one rak‘ah and sit down, then build upon the prayer of the people. When he has led them in four rak‘ahs, he should sit and recite the tashahhud, then take the hand of another man and put him forward. When that person says salam, he should stand up and complete his missed rak‘ah.

Ibrahim was asked about a person who was appointed as the deputy by the imam after missing one rak'ah, so what should he do? He replied that he should lead the people in the remaining prayer, and when he completes the prayer, he should bring forward a person who has performed that rak'ah; when he finishes with salam, then this person should stand up and complete his prayer.

Hazrat Ibn Abbas (may Allah be pleased with them both) narrates that when the Messenger of Allah (peace and blessings be upon him) came to Hazrat Abu Bakr during the prayer in his final illness, he started the recitation from the point where Hazrat Abu Bakr had reached.