Likutei Moharan 49:3/ליקוטי מוהר"ן מ״ט:ג׳

13. This is also the aspect of the heh. It was a dalet, but turned around and became <through this the aspect of> a heh. It was a DaLet —this connotes DaLah (poverty stricken) and poor. In other words, this is when a person clogs up his heart with foolishness—for “poor” is only in knowledge (Nedarim 41a) —so that it is then the aspect of dalet. But when he sanctifies his thoughts, there being no sanctity with less than ten (Megillah 23b), this is the yod that he draws into the dalet so that it becomes a heh.