كتاب الحج
15  
The Book of Pilgrimage
(43)
Chapter: Clarifying that Sa'i between As-safa and Al-Marwah is a pillar of Hajj, without which Hajj is not valid
(43)
باب بَيَانِ أَنَّ السَّعْىَ بَيْنَ الصَّفَا وَالْمَرْوَةِ رُكْنٌ لاَ يَصِحُّ الْحَجُّ إِلاَّ بِهِ ‏
Sahih Muslim 1278

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.
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنْ عَاصِمٍ، عَنْ أَنَسٍ، قَالَ كَانَتِ الأَنْصَارُ يَكْرَهُونَ أَنْ يَطُوفُوا بَيْنَ الصَّفَا وَالْمَرْوَةِ حَتَّى نَزَلَتْ ‏{‏ إِنَّ الصَّفَا وَالْمَرْوَةَ مِنْ شَعَائِرِ اللَّهِ فَمَنْ حَجَّ الْبَيْتَ أَوِ اعْتَمَرَ فَلاَ جُنَاحَ عَلَيْهِ أَنْ يَطَّوَّفَ بِهِمَا‏}
Reference : Sahih Muslim 1278
In-book reference : Book 15, Hadith 290
USC-MSA web (English) reference : Book 7, Hadith 2928
  (deprecated numbering scheme)