Reference for Menachot 169:3
וכולן אינן באות אלא מן המובחר כו': אמרי ליה יוחנא וממרא למשה תבן אתה מכניס לעפריים אמר להו אמרי אינשי למתא ירקא ירקא שקול:
and Mamre<span class="x" onmousemove="('comment',' They were the chief magicians in Egypt in the time of Moses. They are mentioned in Jewish literature also under the name of Jannes and Jambres. V. J. E. VIII, p. 71.');"><sup>4</sup></span> said to Moses, 'Wouldst thou carry straw to Hafaraim? '<span class="x" onmousemove="('comment',' So MS.M. and other MSS.; in cur. edd. 'Afraim, v. note on this word in Mishnah, supra p. 506. Hafaraim was a town where apparently there was a plentiful supply of straw, and so it became proverbial to describe wasted efforts as 'carrying straw to Hafaraim'. (Cf. to carry coals to Newcastle') . As Egypt was reputed to be a land of magic and sorcery these magicians thus taunted Moses when he performed his wonders before the Pharaoh.');"><sup>5</sup></span>