Abu Dawud Book 1, Hadith Number 81.

Chapter : Performing ablution with water left over after a dog has drunk of it.

Narated By Humayd al-Himyari : Humayd al-Himyari reported: I met a person (among the Companion of Prophet) who remained in the company of the Prophet (PBUH)for four years as AbuHurayrah remained in his company. He reported: The Apostle of Allah (PBUH) forbade that the female should wash with the water left over by the male, and that the male should wash with the left-over of the female.

The version of Musaddad adds: “That they both take the handful of water together.”