Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: One day I climbed onto the roof of our house and saw the Messenger of Allah (peace and blessings be upon him) sitting on two bricks to relieve himself, and he (peace and blessings be upon him) had his face towards Syria and his back towards the qiblah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 437