It is narrated from Sayyiduna Ibn Amr, may Allah be pleased with him, that whoever sends blessings upon the Noble Prophet, peace and blessings be upon him, once, Allah and His angels send mercy upon him seventy times.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6754
Hadith Gradingحکم دارالسلام:إسناده ضعيف، ابن لهيعة سيئ الحفظ وعبد الرحمن بن مريح مجهول