وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ أَبَا بَكْرٍ، وَعُمَرَ، كَانَا يَفْعَلاَنِ ذَلِكَ ‏.‏

Yahya related to me from Malik that he had heard that Abu Bakrand Umar used to do that. Translation Not Available

Book Ref: Muwatta Imam Malik Book 10 Hadith 434
Web Ref:  Muwatta Imam Malik Book 10 Hadith 4