In the book 'Be mindful of Allah regarding your mothers' Shaykh Raslan mentioned a narration (athar) where Ibn Abbas رضي الله عنه asked a man who killed someone he wanted to marry:
"Is your mother alive?"
Then further after questioning the man he said:
"Indeed I don't know of any action which brings one more closer to Allah than showing goodness to one's mother" (Authenticated by al-albani)
Shaykh Raslan mentioned:
Indeed showing goodness to one's mother brings the sinning person more closer to Allah than any other action of obedience. So for this reason Ibn Abbas said:
"Indeed I don't know of any action which brings one more closer to Allah than showing goodness to ones mother"
So Ibn Abbaas advised the killer to be diligent in showing goodness to his mother in order that Allah may forgive him of what he did previously of the crime of killing.
TN: So if this is the case in terms of majors sins such as killing then what about sins less than that.
Source: Allah Allah fi ummataatikum page 14
Translated and compiled by Abu Anas Atif Hasan