Reference for Bava Kamma 198:4

ורבי יהודה הנשיא אומר באמת אמרו בין בשכר שעשיתי עמך ובין בשכר שאעשה עמך אינה מקודשת ואם הוסיף לה נופך משלו מקודשת

This was also the difference between the following Tannaim, as taught: [If a man says,] 'In consideration of the hire for the work I have already done for you<span class="x" onmousemove="('comment',' The article having been already returned to her. ');">⁵</span> [be betrothed to me],'<span class="x" onmousemove="('comment',' This was spoken to a prospective wife. ');">⁶</span>

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