Nafi' narrated: When Ibn Umar (may Allah be pleased with them both) intended to enter ihram, he would come to Dhu al-Hulayfah and spend the night there. Then, when morning came, he would mount his riding camel, and when it stood up straight with him, he would call out the Talbiyah. And he would state that the Messenger of Allah (peace and blessings be upon him) used to do the same.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13363