At-Tabaraani in Al-Mu’jam Al-Kabeer and Al-Bayhaqi in Shu’ab Al-Eemaan reported from Abu Umaamah(r.a) 

 that the Prophet(saw)  said: “The angel on the left-hand side (who records sins) holds up his pen (refrains from writing down) for six hours after Muslim sins. If the person regrets it and asks Allah for forgiveness, he casts it aside (does not write it down); otherwise, it is written down as one a (bad deed).”

Shaykh Al-Albaani classified it as Hasan in Saheeh Al-Jaami’ As-Sagheer, and he quoted it in As-Silsilah As-Saheehah.

Allah knows best.