Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "It is not lawful for a Muslim to cut off relations with his Muslim brother for more than three days, such that they meet yet each holds back; and the better of the two is the one who begins with the greeting of salam."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20027