Musannaf Ibn Abi Shayba 27:154

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