Sahih Bukhari, Hadith No. 1433

Narrated Abu Huraira (R.A): The Prophet (S.A.W) said, six are the rights of a Muslim over another Muslim. It was said to him: Allah's Messenger, what are these? Thereupon he said: when you meet him, offer him greetings; when he invites you to a feast, accept it; when he seeks your council, give him; and when he sneezes and says: Al-Hamdu Lillah (praise be to Allah), you say Yarhamuk Allah (may Allah show mercy to you); and when he falls ill, visit him; and when he dies, follow his bier.

Narrated Ibn Abbas (R.A): The Prophet (S.A.W) said, "No good deeds done on other days are superior to those done on these (first ten days of Dhul Hijja)." Then some companions of the Prophet (S.A.W) said, "Not even Jihad?" He replied, "Not even Jihad, except that of a man who does it by putting himself and his property in danger (for Allah's sake) and does not return with any of those things".

Narrated Anas bin Malik (R.A): Allah's Messenger (S.A.W) said, "Do not hate one another, nor be jealous of one another, and do not desert one another, but O Allah's worshipers! Be Brothers! And it is unlawful for a Muslim to desert his brother Muslim (and not to talk to him) for more than three nights".