I saw the Messenger of Allah ﷺ say the takbir at every lowering, rising, standing, and sitting, and he would give the salam to his right and to his left until the whiteness of his cheeks, or one cheek, could be seen. I also saw Abu Bakr and Umar doing the same.
حدثنا يحيى عن زهير قال حدثني أبو إسحاق عن عبد الرحمن بن الأسود عن الأسود وعلقمة
أنا رأيت رسول الله ﷺ يكبر في كل خفض ورفع وقيام وقعود ويسلم عن يمينه وعن يساره حتى يرى بياض خديه أو خده ورأيت أبا بكر وعمر يفعلان ذلك
Its isnad is sahih. Abdul-Rahman bin Aswad bin Yazid bin Qays Nakhai is trustworthy, one of the finest of men, and the authors of the six books cited him. His father, Aswad bin Yazid, was a trustworthy successor, a jurist and an ascetic. Alqama is Ibn Qays, mentioned previously at 3563, and he was the paternal uncle of Aswad bin Yazid. The hadith was narrated by Tirmidhi and Nasai, as noted in al-Muntaqa, 935.