According to 'Abdullah ibn 'Umar, the Prophet PBUH, addressing the people on the occasion of farewell pilgrimage, exhorted them to listen carefully to what he had to say:
'All Muslims are brothers. They constitute one brotherhood. Nothing belonging to one Muslim can become legitimate property of another, unless it has been freely and willingly given. Do not, therefore, do injustice to your own selves. O God, have I conveyed your message? Woe betide you. When I am gone, do not become infidels and start killing each other.'
HADITH OF AL-BUKHARI