مُوَطَّأُ مَالِكٍ
Muwatta Malik 58
Purity
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم سُئِلَ عَنْ الاِسْتِطَابَةِ فَقَالَ أَوَلاَ يَجِدُ أَحَدُكُمْ ثَلاَثَةَ أَحْجَارٍ .
Yahya related to me from Malik from Hisham ibn Urwa from his father that the Messenger of Allah, (ﷺ), was asked about cleaning after excretion. He replied, "Are any of you unable to find three stones?"
Arabic/English book reference: Book 2, Hadith 28