حِصْنُ الْمُسْلِمِ
Hisn al-Muslim 223
Fortress of the Muslim (Hisn al-Muslim)
Excellence of sending prayers upon the Prophet (ﷺ)
وَقَالَ صلى الله عليه وسلم: (مَا مِنْ أَحَدٍ يُسَلِّمُ عَلَيَّ إِلاَّ رَدَّ اللَّهُ عَلَيَّ رُوحِيَ حَتَّى أَرُدَّ عَلَيْهِ السَّلاَمَ)
-- The Prophet (ﷺ) 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." Reference: Abu Dawud (no. 2041). Al-Albani graded it good in Sahih Abu Dawud 1/383.
Hisn al-Muslim, 223