A Muslim is a brother of another Muslim - Bukhari
Allah's Apostle said, "A Muslim is a brother of another Muslim, so he should not
oppress him, nor should he hand him over to an oppressor. Whoever fulfilled the
needs of his brother, Allah will fulfill his needs; whoever brought his (Muslim)
brother out of a discomfort, Allah will bring him out of the discomforts of the
Day of Resurrection, and whoever screened a Muslim, Allah will screen him on the
Day of Resurrection . "
Sahih Bukhari , Book 43,