The Prophet ﷺ said that a person waking from sleep should not dip his hand into the vessel until he has washed it three times.
The prohibition concerns dipping the unwashed hand into stored water. The explanation refers to uncertainty about where the hand may have been during sleep. It does not mean that the hand is certainly impure in every case.
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Sunnahs of Wudu and Their Juristic Rulings
The Prophet ﷺ said that a person waking from sleep should not dip his hand into the vessel until he has washed it three times.
The prohibition concerns dipping the unwashed hand into stored water. The explanation refers to uncertainty about where the hand may have been during sleep. It does not mean that the hand is certainly impure in every case.