Sunan an-Nasa'i, Volume 2, Book 13, Hadith 1320 (DarusSalam) ⓘ

It was narrated that 'Abdullah said: "I saw the Messenger of Allah saying the takir every time he went down or came up, or stood or sat, and he said the salam to his right and to his left: As-salamu 'alaykum wa rahmatullah, as-salamu alaykum wa rahmatullah (peace be upon you and the mercy of Allah, peace be upon you and the mercy of Allah) until the whiteness of his cheek could be seen. And I saw Abu Bakr and 'Umar, may Allah (WT) be pleased with them, doing likewise."

أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا مُعَاذُ بْنُ مُعَاذٍ، قَالَ حَدَّثَنَا زُهَيْرٌ، عَنْ أَبِي إِسْحَاقَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الأَسْوَدِ، عَنِ الأَسْوَدِ، وَعَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ، قَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يُكَبِّرُ فِي كُلِّ خَفْضٍ وَرَفْعٍ وَقِيَامٍ وَقُعُودٍ وَيُسَلِّمُ عَنْ يَمِينِهِ وَعَنْ شِمَالِهِ ‏ "‏ السَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللَّهِ السَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللَّهِ ‏" ‏ ‏.‏ حَتَّى يُرَى بَيَاضُ خَدِّهِ وَرَأَيْتُ أَبَا بَكْرٍ وَعُمَرَ - رضى الله عنهما - يَفْعَلاَنِ ذَلِكَ ‏.‏