Sahih Muslim Book 7, Hadith Number 2928.

Chapter : Sa’i between al-Safi’ and at-Marwi is essential rite of Hajj and Hajj is not complete without it.

Anas (Allah be pleased with him) reported that the Ansar felt reluctant that they should circumambulate between al-Safa’ and al-Marwa until it was revealed: “Verily al-Safa’ and al-Marwa are among the Signs of Allah”; so whoever performs Hajj or ‘Umra, for him there is no harm that he should circumambulate between them.