Musannaf Ibn Abi Shayba 3:6322

Hushaym narrated to us, he said: Husayn informed us, from Yazid al-Raqashi, that an angel is appointed over whoever sends blessings upon the Prophet, may Allah bless him and grant him peace, to convey to the Prophet, may Allah bless him and grant him peace, that: "So-and-so from your nation has sent blessings upon you."