Sayyiduna Abu Umamah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) said: "Whoever sends blessings upon me once, Allah will send ten mercies upon him. An angel is appointed over that blessing until he conveys it to me."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7580