What is the evidence for the obligation of a latecomer to repeat the prostration of forgetfulness that he performed with the Imam if the latecomer joined in the Imam's forgetfulness, but not to repeat it if he did not join in the forgetfulness? And how does the latecomer know the time of the Imam's forgetfulness? And is the latecomer required to perform the prostration of forgetfulness if he forgets while praying behind the Imam?

If the Imam makes a mistake and performs the prostration of forgetfulness (sujud al-sahw) before the salām, the latecomer (masbuq) must follow him. The latecomer is then required to prostrate again after completing his prayer, unless the Imam's mistake occurred before the latecomer joined him. However, if the Imam prostrates after the salām, the latecomer should not prostrate with him, but should prostrate after his own salām if the Imam's mistake occurred after the latecomer joined him. The Imam bears the mistake of the follower (ma'mum) as long as the follower is praying behind him.