From Sahih Muslim (Hadith 606):
Salman reported that it was said to him:Your Apostle (ﷺ) teaches you about everything, even about excrement. He replied: Yes, he has forbidden us to face the Qibla at the time of excretion or urination, or cleansing with right hand or with less than three pebbles, or with dung or bone
Reference: Muslim 606