Mukhtasar Bukhari

Narrated by Abdullah bin Mas'ud (may Allah be pleased with him): The Prophet (peace and blessings of Allah be upon him) said: Abusing a Muslim is wickedness and fighting him is disbelief.

Narrated Sayyiduna Ubadah bin Samit (may Allah be pleased with him): The Messenger of Allah (peace and blessings of Allah be upon him) came out (once) to inform the people about the (exact) Night of Qadr, but (coincidentally at that time) two Muslims were fighting with each other. So the Prophet (peace and blessings of Allah be upon him) said: I came out to inform you about the (exact) Night of Qadr, but since so-and-so and so-and-so were fighting, (the definite knowledge of it) was taken away (from the world), and perhaps this is better for you. (Now) seek the Night of Qadr in the twenty-seventh, twenty-ninth, and twenty-fifth (nights) of Ramadan.