The Prophet (ﷺ) used to say when throwing pebbles in three jamarat:

اَللَّهُ أَكْبَرُ

Allahu 'Akbar

Allah is the Most Great. Then he would move forward a little and stand facing the Qibla and would do Dua with both hands raised in the first Jamra and the second Jamra. But at the time of throwing every pebble at Jamratul Akbaba, he would say ‘Allahu Akbar’ and return without staying there.

Reference: Bukhari: 1751