It is narrated from Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with them both) that Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) said: "O Messenger of Allah, advise me." He (peace and blessings be upon him) said: "Worship Allah and do not associate anything with Him." He said: "O Messenger of Allah, tell me more." He (peace and blessings be upon him) said: "When you do something bad, then do good (after it)." He said: "O Messenger of Allah, tell me more." He (peace and blessings be upon him) said: "Be steadfast, and keep your character good."
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated this hadith from Sa'id bin Abi Sa'id al-Mahri except Harmalah bin Imran."
Hadith Referenceالمعجم الأوسط / باب الميم / 8747
Hadith Takhrij«أخرجه ابن حبان فى «صحيحه» برقم: 524، والحاكم فى «المستدرك» برقم: 7711، والطبراني فى «الكبير» برقم: 58»