Tawus (may Allah have mercy on him) said: I saw Ibn Umar (may Allah be pleased with them both) performing sa'i at the House, and he had tied a cloth around his stomach.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9070
Nafi' (may Allah have mercy on him) said that Ibn Umar (may Allah be pleased with them both) had not knotted the cloth; rather, he had tucked its end into his waist-wrap.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9071
It is narrated from Ibn Jurayj (may Allah have mercy on him) that the Messenger of Allah (peace and blessings be upon him) saw a man girded with a two-coloured rope, and he said twice: "Remove the rope."
This is munqati' (has a broken chain). Ibn Abi Dhi'b also narrated it from Salih bin Hassan from the Prophet (peace and blessings be upon him), and that too is munqati', except that each of them is strengthened by the other, then by the report of Ibn Umar that has already passed, and then by the fact that when it is knotted it takes the ruling of stitched clothing.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9072