وَغَسْلِ الْإِنَاءِ مِنْ وُلُوغِ الْكَلْبِ «وَفِيهِ دَلِيلٌ عَلَى نَقْضِ قَوْلِ مَنْ زَعَمَ أَنَّ الْمَاءَ طَاهِرٌ، وَالْأَمْرُ بِغَسْلِ الْإِنَاءِ تَعَبُّدٌ، إِذْ غَيْرُ جَائِزٍ أَنْ يَأْمُرَ النَّبِيُّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ بِهَرَاقَةِ مَاءٍ طَاهِرٍ غَيْرِ نَجِسٍ»
This contains evidence against the position of those scholars who claim that water is pure and washing the vessel is a devotional act, because it is impossible that the Prophet (peace be upon him) would command to pour away (and waste) pure, non-impure water.