The Prophet (peace and blessings be upon him) said:
"Cleaning oneself after relieving oneself (istinja) should be done with (at least) three stones, provided there is no dung (or any impure thing) among them."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 2773
Hadith Gradingالألبانی:حسن
Hadith Takhrij[طب] عن خزيمة بن ثابت. صحيح أبي داود ٣١: حم، د، ابن ماجه، هق.