Sunan an-Nasa'i 1142
It was narrated from 'Abdur-Rahman bin Al-Aswad from his father-and Alqamah-that:
Abdullah said: "I saw the Messenger of Allah (ﷺ) say the Takbir every time he went down and got up, or stood or sat; he said the Salam on his right and his left: 'As-salamu alaykum wa rahmatulah (peace be upon you and the mercy of Allah ),' until the whiteness of his cheek could be seen." He said: "And I saw Abu Bakr and 'Umar, may Allah (SWT) be pleased with them both, doing the same."
أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ أَنْبَأَنَا الْفَضْلُ بْنُ دُكَيْنٍ، وَيَحْيَى بْنُ آدَمَ، قَالاَ حَدَّثَنَا زُهَيْرٌ، عَنْ أَبِي إِسْحَاقَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الأَسْوَدِ، عَنْ أَبِيهِ، 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 ‏"‏ ‏.‏ حَتَّى يُرَى بَيَاضُ خَدِّهِ ‏.‏ قَالَ وَرَأَيْتُ أَبَا بَكْرٍ وَعُمَرَ - رضى الله عنهما - يَفْعَلاَنِ ذَلِكَ ‏.‏