Reference for Menachot 64:3
הא מורידין עושין והא בעיא שרטוט דאמר רב מניומי בר חלקיה אמר רב חמא בר גוריא אמר רב כל מזוזה שאינה משורטטת פסולה ורב מנימין בר חלקיה דידיה אמר שרטוט של מזוזה הלכה למשה מסיני
But it must be written on ruled lines!<span class="x" onmousemove="('comment',' Whereas the Scriptural portions of the tefillin are not written on ruled lines, so that the portions of the tefillin cannot serve for the mezuzah.');"><sup>3</sup></span> For R'Minyomi B'Hilkiah said in the name of R'Hama B'Goria who said it in the name of Rab, A mezuzah that is not written on ruled lines is invalid. Moreover, R'Minyomi B'Hilkiah on his own authority said that [the rule for writing] the mezuzah on ruled lines is a law handed to Moses at Sinai! - Tannaim differ on this point, for it was taught: R'Jeremiah said in the name of our Master:<span class="x" onmousemove="('comment',' Rabbi (?)');"><sup>4</sup></span>