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: 6212
This hadith has been transmitted on the authority of Zuhri with a slight variation of wording (and the words are):" The one turning away and the other turning away when they meet and one avoids the other and the other also avoids him."