Yahya related to me from Malik from Hisham ibn Urwa that hisfather would never do two sets of seven tawafs together withoutpraying between them. After every seven tawafs he would pray tworakas, sometimes at the maqam of Ibrahim, and sometimes elsewhere.Malik was asked whether a man doing voluntary tawaf could, tomake it easier on himself, join two or more sets of seven circuits andthen pray whatever he owed for those sets of seven, and he said, "Heshould not do that. The sunna is that he does two rakasafter everyseven circuits."Malik said, about someone who began doingtawaf and then forgot how many he had done and did eightor ninecircuits, "He should stop when he knows that he has done more than theright number and then pray two rakas,and he should not count the onesthat he has done in excess. Neither should he build on the nine thathe has done and then pray the rakas for the two sets of seven circuitstogether, because the sunna is that you pray two rakas after everyseven circuits."Malik said that someone who was in doubtabout his tawaf after he had prayed the two rakas of tawaf should goback and complete his tawaf until he was certain of how much he haddone. He should then repeat the two rakas, because prayer when doingtawaf was only valid after completing seven circuits."Ifsome one breaks his wudu either while he is doing tawaf, or when hehas finished tawaf but before he has prayed the two rakas of tawaf, heshould do wudu and begin the tawaf and the two rakas afresh. Breakingwudu does not interrupt say between Safa and Marwa, but a personshould not begin say unless he is pure by being in wudu."
USC-MSA web (English) reference: Book 20, Hadith 117
Arabic reference: Book 20, Hadith 820