Sahih al-Bukhari 1552
Sahih al-Bukhari · Book 25: Hajj (Pilgrimage) · Reciting Talbiya when one has mounted his mount and it stood up straight (ready to set out)
Narrated Ibn `Umar:
حَدَّثَنَا أَبُو عَاصِمٍ ، أَخْبَرَنَا ابْنُ جُرَيْجٍ ، قَالَ أَخْبَرَنِي صَالِحُ بْنُ كَيْسَانَ ، عَنْ نَافِعٍ ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ أَهَلَّ النَّبِيُّ صلى الله عليه وسلم حِينَ اسْتَوَتْ بِهِ رَاحِلَتُهُ قَائِمَةً.
The Prophet (p.b.u.h) recited Talbiya when he had mounted his Mount and was ready to set out.