Yahya related to me from Malik from Hisham ibn Urwa that hisfather said that the Messenger of Allah, may Allah bless him and granthim peace, once said to Abd ar-Rahman ibn Awf, "What do you do, AbuMuhammad, when saluting the corner?" and Abd ar-Rahman said,"Sometimes I salute it, and sometimes I don't." The Messenger ofAllah, may Allah bless him and grant him peace, said, "You are right."
USC-MSA web (English) reference: Book 20, Hadith 114
Arabic reference: Book 20, Hadith 817