Al-Kāfi - The Book of Prayer

Chapter: Tashahhud after the First Two Rak‘at and After the Fourth Rak‘at and Al-Taslim 7ـ وَبِهَذَا الإِسْنَادِ عَنِ ابْنِ ٠ُسْكَانَ عَنْ أَبِي بَصِيرٍ قَالَ قَالَ أَبُو عَبْدِ الله (عَلَيْهِ الْسَّلا٠) إِذَا كُنْتَ فِي صَفٍّ فَسَلِّ٠ِينِكَ وَتَسْلِي٠َةً عَنْ يَسَارِكَ لأَنَّ عَنْ يَسَارِكَ ٠ُ عَلَيْكَ وَإِذَا كُنْتَ إِ٠ُسْتَقْبِلُ الْقِبْلَةِ.

If you are the Imam, then say Salam (the phrase of offering greeting of peace) facing al-Qiblah (al-Ka‘bah).’” صحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (5/163))