It is narrated from Sayyiduna al-Hakam bin Sufyan al-Thaqafi, or Sufyan bin al-Hakam, (may Allah be pleased with him) that "Whenever the Prophet (peace and blessings be upon him) performed ablution, he would take a handful of water and sprinkle it over his private part."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3161