Reference for Pesachim 24:6
ורבא אליבא דר"מ דאמר אדם טועה שתי שעות חסר משהו מתחילת ה' לא ניכול ה' חמה במזרח וז' חמה במערב
Now according to Raba who maintains [that] on R'Meir's view a man may err in two hours less a trifle, let us not eat [leaven] from the beginning of the fifth [hour]? - In the fifth [hour] the s in the east, while in the seventh the sun is in the west.<span class="x" onmousemove="('comment',' And the interdict of leaven commences in the seventh only; hence there is no possibility of error.');"><sup>7</sup></span> If so, let us eat during the sixth [hour] too? - Said R Adda B'Ahabah: In the sixth the sun stands in the meridian.<span class="x" onmousemove="('comment',' Lit., 'between the corners', - equidistant from the east and the west, and so an error is possible.');"><sup>8</sup></span>