Musnad Ahmad 298:0

Hisham ibn ‘Amir al-Ansari said: The Messenger of Allah (ﷺ) said: "It is not lawful for a Muslim to desert his brother for more than three nights. If they meet, this one turns away and that one turns away, and the better of the two is the one who initiates the greeting." He also said: "The blood of a Muslim is not lawful except for one of three: a soul for a soul, a married person who commits adultery, or a person who apostatizes from his religion after having accepted Islam."