Musnad Ahmad 30:1932

'Affan narrated to us, Wuhayb narrated to us, Suhayl narrated to us, from his father, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "The gates of heaven are opened every Monday and Thursday. On that day, every servant who does not associate anything with Allah is forgiven, except for a man between whom and his brother there is enmity. It is said: 'Delay these two until they reconcile.'"