Sayyiduna Amir bin Rabi'ah (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "Whoever sends blessings upon me once of his own accord, Allah Almighty will, in return, send ten mercies upon him."
(Allamah al-Haythami says:) I say:
Ibn Majah recorded it, but it does not contain the words: "of his own accord."
Al-Bazzar recorded it; its chain contains Asim bin Ubaydullah, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأدعية / 17289