Likutei Moharan 35:3/ליקוטי מוהר"ן ל״ה:ג׳

13. Now, renewal of the intellect—i.e., renewal of the soul—is by means of sleep, as is brought in the holy Zohar (I, 213b) <based on> “They are renewed every morning; abundant is Your faithfulness” (Lamentations 3:23). For when the mochin (mentalities, intellect) are overtaxed, then, as we see empirically, they are renewed by means of sleep.

2This is why we recite the blessing “Who gives strength to the weary.” Earlier they were exhausted, but now they are revitalized.

3And while sleeping, the mentalities—i.e., the soul—enter into faith; this being the aspect of “They are renewed every morning; <abundant is Your faithfulness>,” as is brought in the holy Zohar.