When Sayyiduna Ali (may Allah be pleased with him) fought against the people of Nahrawan, he gave the order regarding a specific man to search for him. The people found him among the slain in a pit. They brought him out, and Sayyiduna Ali (may Allah be pleased with him) turned towards his companions and said: If you had not gone to excess, I would have told you the promise that Allah has made, through the tongue of the Prophet (peace and blessings be upon him), to those who kill them. The narrator says: I asked him, "Did you really hear any statement from the Prophet (peace and blessings be upon him) in this regard?" He replied: Yes! By the Lord of the Ka'bah.
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 983
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد حسن، وانظر ما قبله