Abu Humayd al-Saidi reported, while in the company of ten of the Prophet's ﷺ companions, among them Abu Qatada, describing the prayer of the Prophet ﷺ. The narration includes the following.Then he would return, meaning to prostration, then rise and say, "Allahu Akbar." Then he would fold his leg and sit upon it evenly until he settled back, so that every bone returned to its place evenly.
عن ابي حميد الساعدي في عشرة من اصحاب النبي ﷺ فيهم ابو قتادة فذكر الحديث في صفة صلاة النبي ﷺ وفيه: ثم يعود يعني الي السجود، ثم يرفع فيقول: الله اكبر، ثم يثني رجله فيقعد عليها معتدلا حتى يرجع، او يقر كل عظم موضعه معتدلا.
Bayhaqi (2/123) narrated it, and this is his wording, from his teacher Hakim Abu Abdullah, who said, Abul-Abbas Muhammad bin Yaqub narrated to us, Muhammad bin Sinan narrated to us, Abu Asim narrated to us, from Abdul-Hameed bin Jafar, who said, Muhammad bin Amr bin Ata narrated to me, saying, I heard Abu Humayd Saadi, among ten of the Prophet'sﷺ companions, mention something similar. Bayhaqi pointed to this in Marifah (3/42), saying, "We have narrated the sitting of rest in the hadith of Abu Humayd Saadi," though he did not mention it in the chapter itself.This hadith was also narrated by Abu Dawud (963) through two routes, from Imam Ahmad bin Hanbal, who said Abu Asim Dahhak bin Makhlad narrated to us, and from Musaddad, from Yahya (that is, Ibn Saeed), both of them from Abdul-Hameed bin Jafar with this chain, within a hadith describing the Prophet'sﷺ prayer. However, the point of evidence is not clear to me except for his statement, "He spreads open the toes of his feet with a fatkh (using the letter kha) when he prostrates," then he says, "Allahu Akbar," and rises, and folds his left leg and sits upon it, then does the same with the other leg.But Ibn Hajar affirmed that all the narrations from Abu Humayd did not agree in denying the sitting of rest. In fact, Abu Dawud also narrated it from another route from him affirming it, in response to Tahawi, who claimed that the hadith of Abu Humayd contained no mention of it. See Fath al-Bari (2/302).I say, this is how Abu Dawud narrated the hadith of Abu Asim from Imam Ahmad, but I did not find it in the Musnad. Rather, Ahmad narrated it in his Musnad (23599) from Yahya bin Saeed, from Abdul-Hameed bin Jafar with this chain, describing the Prophet'sﷺ prayer, and the point of evidence in it is his statement, "Then he went down prostrating and said, 'Allahu Akbar,' then he held his arms away from his sides and kept his upper arms away from his belly, and spread open the toes of his feet, then he folded his left leg and sat upon it, and settled until every bone returned to its place. Then he went down prostrating and said, 'Allahu Akbar,' then he folded his leg and sat upon it until every joint returned to its place, then he rose and did the same in the second rakat."Tirmidhi (304) also narrated it from Muhammad bin Bashshar and Muhammad bin Muthanna, who both said, Yahya bin Saeed Qattan narrated to us, and he mentioned the description of the Prophet'sﷺ prayer, with the same point of evidence.As for his statement "fatakha" with the letter kha, meaning he spread open the toes of his feet, that is, he set them upright and pressed down on the joints of them, and folded them toward the inside of the foot. The root meaning of fatakh is softness, and from this the eagle is called "fatkha," because when it swoops down it folds its wings. So it is stated in Nihayah.As for what appears in some narrations as "fataha" with the letter ha, some scholars consider it a scribal error, even though its meaning is close to the other.