Reference for Makkot 40:6

והמקיף פאת ראשו וכו': ת"ר פאת ראשו סוף ראשו ואיזהו סוף ראשו זה המשוה צדעיו לאחורי אזנו ולפדחתו

And one who rounds the corners of his head. etc.: The rabbis taught in a baraisa, The corners of his head are the extremities of his head. And what are the extremities of his head? This refers to someone who smooths out his side from behind his ears to his forehead.

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