Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) only did this (walking briskly in tawaf, that is, raml) to show the polytheists his strength; so now whoever wishes may do it and whoever wishes may leave it.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11241