Ibn Jurayj (may Allah have mercy on him) narrated: I asked Ata': A man vowed that he would perform seven circuits of tawaf on his knees? He said: Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: "They were not commanded to perform tawaf crawling; rather, let him perform seven circuits for his knee and seven circuits for his foot." I asked: Did he not order him to give any expiation? He said: "No."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11377