once
وَقَالَ صلى الله عليه وسلم: ((مَا مِنْ أَحَدٍ يُسَلِّمُ عَلَيَّ إِلاَّ رَدَّ اللَّهُ عَلَيَّ رُوحِيَ حَتَّى أَرُدَّ عَلَيْهِ السَّلاَمَ)).
Meaning
The Prophet [PBUH] said: 'No one sends greetings (or prayers of peace) upon me but Allah returns my soul to me so that I may return his greetings
Source and references
Hisn al-Muslim, entry 223.The reference is copied from the edition; separate editorial verification is not complete yet.
Source edition: Fortress of the Muslim. Open source ↗