Sayyiduna Abdullah bin Abbas (may Allah be pleased with him) narrates this statement of the Prophet (peace and blessings be upon him): "When a person performs prayer and is unsure whether he has performed three rak‘ahs or four, he should perform one more rak‘ah and before concluding with salam, he should perform two prostrations of forgetfulness. If it was the fourth rak‘ah, then the two prostrations will disgrace Satan, and if it was the fifth rak‘ah, then the two prostrations will make it even." (Imam Ibn Hibban, may Allah have mercy on him, says:) The narrator named Darawardi made an error in its chain. He said that it is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with him), whereas this narration is actually reported from Sayyiduna Abu Sa‘id Khudri (may Allah be pleased with him). The narrator named Sa‘d bin Ibrahim, since he often narrated hadiths from his memory, it is possible that this was his error.