It is narrated from Shaibah's Umm Walad (may Allah be pleased with her) that she was performing Sa'i between Safa and Marwah when she saw the Messenger of Allah (peace and blessings be upon him) and he was saying: "The Abtah (valley) can only be crossed by running."
Hadith Referenceمسند اسحاق بن راهويه / كتاب المناسك / 301
Hadith Takhrij«سنن ابن ماجه ، كتاب المناسك ، باب السعي بين الصفاء والمروة ، رقم : 2987 . قال الشيخ الالباني صحيح . مسند احمد : 404/6 .»