I saw that Messenger of Allah ﷺ used to ride on his Mount at Dhul Hulaifa and used to start saying, "Labbaik" when the Mount stood upright.
رَأَيْتُ رَسُولَ اللَّهِ ﷺ يَرْكَبُ رَاحِلَتَهُ بِذِي الْحُلَيْفَةِ ثُمَّ يُهِلُّ حَتَّى تَسْتَوِيَ بِهِ قَائِمَةً