بُلُوغُ الْمَرَامِ
Bulugh al-Maram 320
The Book of Prayer
وَعَنْ وَائِلِ بْنِ حُجْرٍ - رضى الله عنه - قَالَ : { صَلَّيْتُ مَعَ اَلنَّبِيِّ - صلى الله عليه وسلم -فَكَانَ يُسَلِّمُ عَنْ يَمِينِهِ : " اَلسَّلَام عَلَيْكُمْ وَرَحْمَةُ اَللَّهِ وَبَرَكَاتُهُ " وَعَنْ شِمَالِهِ : " اَلسَّلَامُ عَلَيْكُمْ وَرَحْمَةُ اَللَّهِ وَبَرَكَاتُهُ } رَوَاهُ أَبُو دَاوُدَ بِسَنَدٍ صَحِيحٍ . [1]
Narrated Wa'il bin Hujr (RA): I prayed with the Prophet (ﷺ) and he would give the Taslim (salutation) to his right side (saying), "Peace be upon you and the mercy and blessings of Allah"; and to his left side (saying), "Peace be upon you and mercy and the blessings of Allah." [Reported by Abu Dawud, with a Sahih (authentic) chain].
Sunnah.com reference: Book 2, Hadith 213