BT Yom 33b(8) :אב{{י}}<ו>רי דרעא אטוטפתא אסיר‏ : it is forbidden to defer (the phylactery) of the arm to the phylactery (of the forehead) [i.e. to put on the latter first]
See the entire entry for ṭōṭəp̄ā, ṭōṭap̄tā n.f. phylactery