When the Messenger of Allah ﷺ finished the morning prayer, the servants of Medina would come to him with their vessels filled with water, and no vessel was brought to him without him dipping his hand into it. Sometimes they would come to him on a cold morning, and he would still dip his hand into the water.
كان رسول الله ﷺ إذا صلى الغداة، جاء خدم المدينة بآنيتهم فيها الماء، فما يؤتى بإناء إلا غمس يده فيها، فربما جاءوه في الغداة الباردة فيغمس يده فيها.
Muslim narrated it in the Book of Virtues (74:2324) from Mujahid bin Musa, Abu Bakr bin Nadr bin Abu Nadr, and Harun bin Abdullah, all of them from Abu Nadr (that is, Hashim bin Qasim), who said, Sulayman bin Mughira narrated to us from Thabit, from Anas, who said, and then he related it.His statement, "he would then dip his hand into it," means so that they might seek blessing through this water.