Zayd bin Aslam زيد بن أسلم · The Book of Forgetfulness (In Prayer)

"We used to pray behind the Messenger of Allah (ﷺ) and we would greet (others) with our hands. He said: 'What is the matter with those who greet (others) with their hands as if they were tails of wild horses? It is sufficient for any one of you to put his hand on his thigh and say: "As-salamu 'alaikum, as-salamu 'alaikum."

The Prophet (ﷺ) led them in prayer and forgot (how many rak'ahs he had prayed), then he prostrated twice, then he said the salam.

"The Messenger of Allah (ﷺ) said the salam after three rak'ahs of 'Asr, then he entered his house. A man called Al-Khibaq stood up and said: 'Has the prayer been shortened, O Messenger of Allah?' He came out angry, dragging his upper garment and said: 'Is he speaking the truth?' They said: 'Yes.' So he stood and prayed that rak'ah, then he said the salam, then prostrated twice, then he said the salam (again)."