Maliks Muwatta Book 20, Hadith Number 131.
Yahya related to me from Malik from Hisham ibn Urwa that Sawda bint Abdullah ibn Umar, who was in the household of Urwa ibn az-Zubayr, set off walking between Safa and Marwa when doing either hajj or an umra. She was a heavy woman and she began when everybody was leaving after the isha prayer, and she still had not completed her circuits when the first call was given for subh, but finished them between the two calls to prayer.
If Urwa saw people doing circuits on riding beasts he would tell them in very strong terms not to do so, and they would pretend to be ill, out of awe of him.
Hisham added, “He used to say to us about them ‘These are unsuccessful and have lost.'”
Malik said, “Someone who forgets say between Safa and Marwa in an umra, and does not remember until he is far from Makka, should return and do say. If, in the meantime, he has had intercourse with a woman, he should return and do say between Safa and Marwa so as to complete what remains of that umra, and then after that he has to do another umra and offer a sacrificial animal.”
Malik was asked about someone who met another man when doing say between Safa and Marwa and stopped to talk with him, and he said, “I do not like anyone to do that.”
Malik said, “If anyone forgets some of his tawaf or is uncertain about it and remembers only when he is doing say between Safa and Marwa, he should stop the say and complete his tawaf of the House apart from that about which he is certain. After that he prays the two rakas of the tawaf, and then begins his say between Safa and Marwa.”