Abu Sa'id al-Khudri said that God's messenger was asked about the purity of the cisterns between Mecca and Medina to which beasts of prey, dogs and asses go down, and replied, “They have what they carry in their bellies, and we have what is left as pure water.” Ibn Majah transmitted it.

وَعَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ سُئِلَ عَنِ الْحِيَاضِ الَّتِي بَيْنَ مَكَّةَ وَالْمَدِينَةِ تَرِدُهَا السبَاع وَالْكلاب والحمر وَعَن الطُّهْرِ مِنْهَا فَقَالَ: " لَهَا مَا حَمَلَتْ فِي بُطُونِهَا وَلَنَا مَا غَبَرَ طَهُورٌ. رَوَاهُ ابْنُ مَاجَه