Musar for Eruvin 191:2
ואיבעית אימא אי דסבירא לן דשבת זמן תפילין דכ"ע לא לעבור בעי כוונה ולא לצאת בעי כוונה
And if you prefer I might reply: If the view had been adopted that Sabbath is a time for tefillin all would have agreed that intention is unnecessary either in respect of transgression<span class="x" onmousemove="('comment',' On the injunction against adding to the commandments. Lit., 'to transgress'.');"><sup>4</sup></span> or in respect of discharging the duty,<span class="x" onmousemove="('comment',' Of the commandment of tefillin. Lit., 'and not to go out (from the obligation) '.');"><sup>5</sup></span> but the point at issue between then here is with reference to the transgression<span class="x" onmousemove="('comment',' On the injunction against adding to the commandments. Lit., 'to transgress'.');"><sup>4</sup></span> when a commandment is performed not at its proper time.