Maliks Muwatta Book 20, Hadith Number 118.
Section : Praying after Subh and Asr when doing Tawaf
Yahya related to me from Malik from Ibn Shihab from Humayd ibn Abd ar-Rahman ibn Awf that Abd ar-Rahman ibn Abd al-Qari mentioned to him that he once did tawaf of the House with Umar ibn al-Khattab after subh and when Umar had finished his tawaf he looked and saw that the sun had not yet risen, so he rode on until he made his camel kneel at Dhu Tuwa, and he prayed two rakas.