Sayyiduna Salman (may Allah be pleased with him) said: "The Messenger of Allah (peace and blessings be upon him) forbade us from facing the qiblah while relieving ourselves, from cleaning ourselves (istinja) with fewer than three stones, and from cleaning ourselves with a bone or dung."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6056