Abu Hanifa and Muhammad emphasize genuine forgetfulness: water in one's luggage was not effectively available to the traveller's awareness at the relevant moment, so the performed prayer stands.
Abu Yusuf emphasizes that the water was in the traveller's own accessible belongings, so repetition is required. The point of difference is the legal consequence of forgetfulness.
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Tayammum Materials, Intention, Nullifiers, and Searching for Water
Abu Hanifa and Muhammad emphasize genuine forgetfulness: water in one's luggage was not effectively available to the traveller's awareness at the relevant moment, so the performed prayer stands.
Abu Yusuf emphasizes that the water was in the traveller's own accessible belongings, so repetition is required. The point of difference is the legal consequence of forgetfulness.