Hazrat Muhammad bin Ata narrates from Sayyiduna Abu Humayd Sa’idi (may Allah be pleased with him) that I heard him saying in the presence of ten companions of the Prophet (peace and blessings be upon him), among whom was also Sayyiduna Abu Qatadah (may Allah be pleased with him). He said that when the Prophet (peace and blessings be upon him) stood for prayer, he would stand completely straight. Then he mentioned the rest of the hadith, saying that then he (peace and blessings be upon him) bent towards the ground for prostration, then said «‏‏‏‏اللهُ أَكْبَرُ» ‏‏‏‏, then he kept his arms away from his sides and spread his toes, then the Prophet (peace and blessings be upon him) folded his left foot and sat on it and sat with calmness until every bone returned to its place, then the Prophet (peace and blessings be upon him) bent for the (second) prostration and said «‏‏‏‏اللهُ أَكْبَرُ» ‏‏‏‏, then the Prophet (peace and blessings be upon him) folded his foot and sat with moderation until every bone returned to its place, then the Prophet (peace and blessings be upon him) stood up.

It is narrated from Sayyiduna Malik bin Huwairith (may Allah be pleased with him) that he saw the Prophet Muhammad (peace and blessings be upon him) performing prayer, and when he (peace be upon him) was in the odd (witr) rak‘ah of his prayer, he would not stand up until he had sat straight.