Musar for Bava Batra 231:8
והא רבי יהושע בן לוי לא אזיל לבי טמיא אלא לבי מאן דשכיב בלא בני דכתיב (ירמיהו כב, י) בכו בכה להולך ואמר רב יהודה אמר רב להולך בלא בן זכר אלא רבי יהושע בן לוי הוא דאמר תלמיד
This is the bone of my tenth son.<span class="x" onmousemove="('comment',' He carried with him a 'bone', which commentators understand to be a tooth, of his tenth dead son when going to comfort those who mourned the loss of a child. Now, if R. Johanan were of the opinion that Ps. LV, 20, has reference to a son, he would not have carried about that which stigmatised him as one who is not God-fearing. ');"><sup>13</sup></span> Thus it is proved that it was R. Johanan who said 'a disciple'. But since R. Johanan said, 'a disciple', R. Joshua b. Levi [must have] said 'a son'! [Is it not a fact,] however, that R. Joshua b. Levi did not go to a house of mourning unless it was the house of him who died without leaving any sons, for it is written, <i>But weep sore for him that goeth away</i>,<span class="x" onmousemove="('comment',' Jer. XXII, 10. ');"><sup>14</sup></span>