Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: In the year that the Messenger of Allah (peace and blessings be upon him) performed Hajj, he (peace and blessings be upon him) was asked about the stoning (rami), and he (peace and blessings be upon him) said: "Allah has made sa'i obligatory upon you, so perform sa'i."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11389