Reference for Yevamot 103:3
פשיטא סד"א כיון דאמר מר העושה מאמר ביבמתו פרחה הימנו זיקת יבמין וחלה עליו זיקת ארוסין ונשואין אימא לאו מצוה קעביד קמ"ל
THIS IS also IN ACCORDANCE WITH THE PRESCRIBED PRECEPT. Is not this obvious? — It might have been presumed that since a Master stated, 'If the levir addressed a ma'amar to his sister-in-law, the levirate bond disappears, and he comes under the bond of betrothal and marriage',<span class="x" onmousemove="('comment',' Supra 29b. It will be noted that the text there slightly differs from the text here. ');"><sup>7</sup></span> he<span class="x" onmousemove="('comment',' Because of the ma'amar he had addressed. ');"><sup>8</sup></span> is not performing the commandment,<span class="x" onmousemove="('comment',' Of the levirate marriage, even though cohabitation had taken place subsequently. ');"><sup>9</sup></span>