It was narrated from 'Amr bin Shu`aib, from his father, from his grandfather, that :

the Messenger of Allah (ﷺ) ruled concerning the stream of Mahzur that the water should be retained until it reached the ankles, then released.

حَدَّثَنَا أَحْمَدُ بْنُ عَبْدَةَ، أَنْبَأَنَا الْمُغِيرَةُ بْنُ عَبْدِ الرَّحْمَنِ، حَدَّثَنِي أَبِي، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَضَى فِي سَيْلِ مَهْزُورٍ أَنْ يُمْسِكَ حَتَّى يَبْلُغَ الْكَعْبَيْنِ ثُمَّ يُرْسِلَ الْمَاءَ ‏.‏