The Messenger of Allah ﷺ said, "Whoever sends blessings upon me once, Allah will send blessings upon him ten times."
حدثنا سليمان أنبأنا إسماعيل أخبرني العلاء عن أبيه
قال رسول الله ﷺ من صلى علي واحدة صلى الله عليه عشرا
No references are available.
Its chain of transmission is sahih. It is found in Muslim 1/306, no. 408, in the Book of Prayer, chapter on sending blessings upon the Prophet, and in Abu Dawud 2/88, no. 1530, in the Book of Prayer, chapter on seeking forgiveness, and in Nasai 3/50, no. 1296, in the Book of Forgetfulness (in Prayer), chapter on the virtue of sending blessings upon the Prophet, and in Tirmidhi 2/355, no. 485, in the Book of Voluntary Prayers, chapter on what has come regarding the virtue of sending blessings upon the Prophet, and he graded it sahih. It has already passed at 7551.