What must one do to return to God and have his sins forgiven, having assaulted his sisters (honor)?

Adultery (zina) is one of the gravest forbidden major sins, and its prohibition becomes even more severe if it is committed with a mahram (a close relative with whom marriage is forbidden). Whoever falls into this abominable act must perform sincere repentance (tawbah nasuhah), abandon the sin, regret it, and firmly resolve never to return to it. This must be accompanied by associating with righteous people, diligently performing religious obligations, persistently seeking forgiveness (istighfar) and performing supererogatory acts of worship, and staying away from places of temptation.