Sunan an-Nasa'i 1323
It was narrated that 'Abdullah said:
"The Messenger of Allah (ﷺ) used to say the salam to his right so that the whiteness of his cheek could be seen, and to his left so that the whiteness of his cheek could be seen."
أَخْبَرَنَا مُحَمَّدُ بْنُ آدَمَ، عَنْ عُمَرَ بْنِ عُبَيْدٍ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي الأَحْوَصِ، عَنْ عَبْدِ اللَّهِ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُسَلِّمُ عَنْ يَمِينِهِ حَتَّى يَبْدُوَ بَيَاضُ خَدِّهِ وَعَنْ يَسَارِهِ حَتَّى يَبْدُوَ بَيَاضُ خَدِّهِ ‏.‏