I saw that Allah's Messenger (ﷺ) used to ride on his Mount at Dhul Hulaifa and used to start saying, "Labbaik" when the Mount stood upright.
Sahih al-Bukhari Book 25, Hadith 2
← Previous Hadith Al-Fadl (his brother) was riding behind Allah's Messenger (ﷺ) and a woman from the tribe of Khath'am came and Al-Fadl started looking at her and she started looking at him. The Prophet (ﷺ) turned Al-Fadl's face to the other side. The woman said, "O Allah's Messenger (ﷺ)! The obligation of Hajj enjoined by Allah on His devotees has become due on my father and he is old and weak, and he cannot sit firm on the Mount; may I perform Hajj on his behalf?" The Prophet (ﷺ) replied, "Yes, you may." That happened during the Hajj-al-Wida (of the Prophet (ﷺ) ).

Sahih al-Bukhari Book 25, Hadith 1 Next Hadith → that Allah's Messenger (ﷺ) started saying, "Labbaik" from Dhul-Hulaifa when his Mount stood upright carrying him .

Sahih al-Bukhari Book 25, Hadith 3