Musannaf Ibn Abi Shayba 8:1616

Abu Bakr narrated to us, he said: Abu Mu'awiyah narrated to us, from Ubayd Allah ibn Umar, from Nafi', from Ibn Umar, that he saw a man in the state of ihram who had sought shade. He said: "Expose yourself to the sun for the sake of the One for whom you have entered into ihram."