Mukhtasar Muslim

It is narrated from Sayyiduna Abu Ayyub Ansari (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: It is not permissible for a Muslim to abandon speaking to his Muslim brother for more than three nights, such that when they meet, one turns his face this way and the other turns his face that way. And the better of the two is the one who initiates the greeting of peace (salam).