It was narrated from ‘Abdullah that the Messenger of Allah (ﷺ) used to say the Salam to his right and his left, until the whiteness of his cheek could be seen (saying):“As-salamu ‘alaikum wa rahmatullah (Peace be upon you and the mercy of Allah).”
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، حَدَّثَنَا عُمَرُ بْنُ عُبَيْدٍ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي الأَحْوَصِ، عَنْ عَبْدِ اللَّهِ، أَنَّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ كَانَ يُسَلِّمُ عَنْ يَمِينِهِ وَعَنْ شِمَالِهِ حَتَّى يُرَى بَيَاضُ خَدِّهِ " السَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللَّهِ " .
IbnMaja
Establishing the Prayer and the Sunnah Regarding Them • Hadith 914