Reference for Yevamot 165:7
ושמואל אמר בקושי וקידוש קושי דתנן
R. Judah said: Any grafting<span class="x" onmousemove="('comment',' And similarly any planting or sinking. ');"><sup>12</sup></span> which takes no root within three days will never take root. R. Jose and R. Simeon stated: [Within] two weeks.<span class="x" onmousemove="('comment',' Sheb. II, 6. ');"><sup>13</sup></span> And, [in reference to this.] R. Nahman stated in the name of Rabbah b. Abbuha that according to him who stated, 'thirty days', thirty and thirty are required;' according to him who stated 'three days', three and thirty are required;<span class="x" onmousemove="('comment',' Since the last thirty days of the eve of the Sabbatical Year are regarded as part of the next Sabbatical Year (v. M.K. 3b). the plant, in order that it may be permitted, must have taken root prior to these last thirty days. ');"><sup>14</sup></span>