Indeed, as-Safa and al-Marwah are among the symbols of Allah. So whoever makes Hajj to the House or performs 'umrah - there is no blame upon him for walking between them. And whoever volunteers good - then indeed, Allah is appreciative and Knowing.  

إِنَّ الصَّفَا وَالْمَرْوَةَ مِنْ شَعَائِرِ اللَّهِ ۖ فَمَنْ حَجَّ الْبَيْتَ أَوِ اعْتَمَرَ فَلَا جُنَاحَ عَلَيْهِ أَنْ يَطَّوَّفَ بِهِمَا ۚ وَمَنْ تَطَوَّعَ خَيْرًا فَإِنَّ اللَّهَ شَاكِرٌ عَلِيمٌ  

I asked Anas bin Malik: "Did you use to dislike to perform Tawaf between Safa and Marwa?" He said, "Yes, as it was of the ceremonies of the days of the Pre-Islamic period of ignorance, till Allah revealed: 'Verily! (The two mountains) As-Safa and Al-Marwa are among the symbols of Allah. It is therefore no sin for him who performs the pilgrimage to the Kaʿba, or performs ʿUmra, to perform Tawaf between them.' " (2.158)  

قُلْتُ لأَنَسِ بْنِ مَالِكٍ ؓ: أَكُنْتُمْ تَكْرَهُونَ السَّعْىَ بَيْنَ الصَّفَا وَالْمَرْوَةِ؟ قَالَ: نَعَمْ، لأَنَّهَا كَانَتْ مِنْ شَعَائِرِ الْجَاهِلِيَّةِ حَتَّى أَنْزَلَ اللَّهُ {إِنَّ الصَّفَا وَالْمَرْوَةَ مِنْ شَعَائِرِ اللَّهِ فَمَنْ حَجَّ الْبَيْتَ أَوِ اعْتَمَرَ فَلاَ جُنَاحَ عَلَيْهِ أَنْ يَطَّوَّفَ بِهِمَا}  

"I asked Anas bin Malik about As-Safa and Al-Marwah, and he said: 'They were among the rites of Jahiliyyah.' He said: 'So during Islam, we refrained from them, then Allah, Blessed and Most High, revealed: Indeed As-Safa and Al-Marwah are of the symbols of Allah. So it is not a sin for those who perform Hajj or 'Umrah to the house to go between them. (2:158)' He said: 'So it is voluntarily then verily, Allah is the All-Recogniser, the All-Knowing. (2:158)'" (Using translation from Tirmidhī 2966)   

كَانَتَا مِنْ مَشَاعِرِ الْجَاهِلِيَّةِ فَلَمَّا كَانَ الْإِسْلَامُ أَمْسَكْنَا عَنْهُمَا فَأَنْزَلَ اللَّهُ {إِنَّ الصَّفَا وَالْمَرْوَةَ مِنْ شَعَائِرِ} [البقرة 158] اللَّهِ فَمَنْ حَجَّ الْبَيْتَ أَوِ اعْتَمَرَ فَلَا جُنَاحَ عَلَيْهِ أَنْ يَطَّوَّفَ بِهِمَا وَمَنْ تَطَوَّعَ خَيْرًا الْآيَةُ