Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.108A.
Ibn Mas’ud and Ibn ‘Umar at the time of throwing pebbles used to say, Allahumma ij’alhu Hajjan mabruran wa zhanban maghfuran “O Allah! Accept this Hajj of ours and pardon our sins”.
Ibrahim said, “The Companions of the Prophet loved that while throwing pebbles at Jamarah Al-Aqabah one should supplicate, “O Allah, accept this Hajj of ours and forgive our sins.” When asked if this supplication should be made at the time of throwing pebbles at each of the other Jamarahs as well he replied in the affirmative.
‘Ata said, “When you throw the pebbles you should utter a takbir (Allahu Akbar) with each throw. This is reported by Sa’id bin Mansur. According to the hadith of Jabir, the Prophet (peace be upon him) uttered Allahu Akbar with each pebble that he threw. The author of Al-Fath says: “There is consensus that there is no harm if someone tails to utter a takbir.”
Salman bin Al-Ahwas reported from his mother that she said. “I saw the Prophet (peace be upon him) riding his mount at Aqabah holding a pebble between his fingers and throwing it, while others were also throwing pebbles with him.” This is reported by Abu Daw’ud.