Reference for Moed Katan 40:7

עני ר' זירא בתריה במה דברים אמורים בחמשה מתי מצוה אבל על אביו ועל אמו קורע והולך

In the case of the [other] five nearest-of-kin [for whom mourning is] obligatory,<span class="x" onmousemove="('comment',' Brother, sister, wife, son and daughter. see next citation.');">⁹</span> but in the case of father or mother one always rends one's garment!' - What you cited [in fact] refers to the deference to be shown to one's father or mother.<span class="x" onmousemove="('comment',' [I.e., though there is no observance of seven days he rends his garments not as an obligation but as a special mark of respect for his parents; v. Nimmuke Yosef.]');">¹⁰</span> Our Rabbis taught: For all [nearest-of-kin] mentioned in the Priest's Section<span class="x" onmousemove="('comment',' Lev. XXI, 1ff.');">¹¹</span>

Jastrow