Reference for Gittin 126:7

התם ספק ממונא לקולא הכא ספק איסורא לחומרא

this Get for my wife, if he desires to retract he may not do so.' What authority do you find for the view that if the husband says 'convey' he is at liberty to retract? R. Nathan; and he lays down that if the husband says 'here you are' he is not at liberty to retract. This proves conclusively that 'here you are' is [according to R. Nathan]<span class="x" onmousemove="('comment',' And a plus forte raison according to Rabbi. ');">⁵</span>

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