Deuteronomy 6:9
And thou shalt write them upon the posts of thy house, and on thy gates.
And thou shalt write them upon the posts of thine house, and on thy gates. To put them in mind of them when they went out and came in, that they might be careful to observe them; this the Jews take literally also, and write in a scroll of parchment this section with some passages; and, as the Targum of Jonathan here, fix them in three places, over against the bed chamber, upon the posts of the house, and on the gate at the right hand of it; and this is what they call the Mezuzah; and the account given of it is this. In a parchment prepared for the purpose, they write the words in Deuteronomy 6:4 and then roll up the parchment, and write on it "Shaddai"; and put it either into a cane (or reed), or else into a like hollow piece of wood, and so fasten it to the wall on the posts of the door at the right hand of entrance; and thus, as often as they go in and out, they make it a part of their devotion to touch this parchment, and kiss it {t}.
{t} Buxtorf. Synag. Jud. c. 31. p. 582, &c. Leo Modena's History of the Rites and Customs of the Jews, par. 1. c. 2. p. 5, 6.