Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.104A.

The total number of pebbles to be thrown is either seventy (70) or forty nine (49). Seven of these are to be thrown on the first Jamarah Al-Aqabah on the 10th of Zhul-Hijjah; twenty one on the 11th day, seven at each of the three jamarahs; and similarly twenty one on the 12th day, throwing seven at each of the three places. The last twenty one pebbles are likewise to be thrown, seven at each of the jamarahs, on the 13th day of Zhul-Hijjah. The total number of these pebbles comes to seventy pebbles.

If a pilgrim throws the pebbles for only three days (the 10th, 11th and 12th of Zhul-Hijjah), and does not throw on the 13th day, he may do so without any harm. In such a case the total number will be forty nine pebbles.

According to Ahmad throwing five pebbles will suffice a pilgrim. ‘Ata says throwing five pebbles will complete his Hajj rites. Mujahid said, “If a pilgrim throws six pebbles he may do so without incurring any penalty.”

Sa’id bin Malik reported: “We returned with the Prophet (peace be upon him) after Hajj. Some of us said they had thrown six, others said they had thrown seven pebbles. But none of us found fault with others for doing so.”