The (hills of) Safa and Marwa are certainly among the symbols of Allah, so whoever is on a pilgrimage (Hajj) to the house (Kaaba) or pays a visit (Umrah) there is no sin on him if he goes around both of them, and whoever does good willingly, then Allah is certainly One Who acknowledges, the Knower.
“Safa Marawah are two hillocks near Kaaba. Hajirah, the wife of Ibrahim (PBH) ran seven times in between these hillocks in search of water for her child Ismael (PBH). She finally found the spring of Zum Zum near Kaaba. In view of this, these two hillocks serve as symbols of the anxiety of Hajirah, her prayer and the acceptance of her prayer. Later on the pagan Arabs placed idols on these hillocks and the pilgrims used to touch them respectfully consequently early Muslims hesitated in going round these places. After the conquest of Mecca by Prophet Muhammed (PBH) and his followers all idols were removed from the sacred Mosque. It is probably in this background that Allah (SWT) is stating that there is no sin in going round these hillocks (now that the idols have been removed).”