It is unlawful for a Muslim to desert his fellow Muslim for more than three nights. As they meet, both of them turn their backs on each other. However, the best of them is the one who starts by greeting the other. [Al-Bukhari]

قال رسول الله -صلى الله عليه وسلم-: «لا يحل لمسلم أن يهجر أخاه فوق ثلاث ليال، يلتقيان: فيُعرض هذا، ويُعرض هذا، وخيرهما الذي يبدأ بالسلام». [صحيح.] - [متفق عليه.]