When beset by an alien thought, feel extremely ashamed because you have been expelled from the King’s palace. 1 Return to the palace with great embarrassment and exceeding humility. To harbor an alien thought is a [grave] sin tantamount to begetting a mamzer, 2 as it is said (Ketuvot 103a) “ewe follows ewe, [as the mother so is her daughter].” 3

Thought has a male and a female aspect. So, too, sound and speech correspond to male and female. 4 The utterance of words of holiness while harboring an alien thought is like a mamzer whose external form is as that of a kosher (fit; legitimate) person but the inner reality is evil. [In our context,] the words spoken are letters of holiness, but the thought [behind them] is evil. For with holy speech [joined to] thoughts of something else you beget a mamzer.

Bear in mind also, that as your thought is wandering among other matters, the Holy One, blessed is He, says: “Why did you come into the teivah (word) when I am not in it?!” 5