Sahih Muslim
The Book of Virtue, Good Manners and Joining of the Ties of Relationship (Kitab Al-Birr was-Salat-I-wal-Adab)
Book Number: 032 / Hadith Number: 6216
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: Don't have estranged relations (with the others) and don't nurse enmity and don't enter into a transaction when the other (has already entered) and be fellow-brothers and servants of Allah.