Performing two Rak´ak after ´Ars prayer

 220. Abu Salamah said that he asked ´Aishah, about the two prostrations (i.e., Rak´ah) which the Messenger of Allah salla alayhi wa sallam used to pray after the ´Ars. She said: ´´He performed them before the ´Ars prayer, but when he was hindered to do so, or he forgot them, then he performed them after the ´Ars and then he was regular on performing them. (It was his habit) that when he (the Prophet salla alayhi wa sallam) performed any prayer, he then continued doing it.´´ Isma´il bin Ja´far said: ´´Ít implies that he always did that.´´