Ata' (may Allah have mercy on him) says that he saw Abdullah bin Abi Rabi'ah (may Allah be pleased with him), who had placed a piece of wood across the middle of his she-camel and put a cloth over it, taking shade with it from the sun while he was in the state of ihram. Ibn Umar (may Allah be pleased with them both) met him and forbade him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9193