As Salaatu wa Salaam 'alaa Rasoolillaah...

Ammaar bin Yaasir, may Allaah be pleased with him, said, "Allaah's Messenger, صلى الله عليه وسلم, said: 

'Indeed Allaah has assigned an angel to my grave. He has given him the named of (all) creation. So no one sends prayers upon me until the Day of Judgment except that he informs me of that person's name and his father's name, (saying): 'This is so and so the son of so and so, he has sent prayers upon you.''"

Reported by al-Bazzaar and others, and our Shaykh al-Albaani, may Allaah have mercy on him, declared it hasan in Sahih al-Targheeb wat-Tarheeb (1667) and also refer to Al-Saheehah (1350)