Abdullah bin Umar (may Allah be pleased with them both) said: When the Messenger of Allah (peace and blessings be upon him) put his foot in the stirrup and his she-camel stood up with him, he began the talbiyah at that point from the mosque of Dhu al-Hulayfah. [Sahih: Bukhari, 2710]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8981