It is narrated from Sayyiduna Salman (may Allah be pleased with him) that (it was said to him): Your Prophet (peace and blessings be upon him) has taught you everything, even the manner of relieving yourselves. The narrator says that he said: "Yes!" Indeed he forbade us "to face the qiblah when relieving ourselves or urinating, or to clean ourselves with the right hand, or to clean ourselves with fewer than three stones, or to clean ourselves with dung or bone."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 430