E. No man, even a Tzaddik, is saved from foreign, and at times forbidden, thoughts: Torah or p. 85a-86b

There is no man who does not suffer from some level of disturbing foreign thoughts [i.e. Machshavos Zaros], each to his level. A person of high spiritual level will have disturbing foreign thoughts fall into his mind in accordance to his level, while a person of low spiritual level will have disturbing foreign thoughts fall into his mind in accordance to his low level. [A foreign thought of a person of high spiritual level, such as a tzaddik, can be considered a Mitzvah or good thought by one of a low-level. However, for the level of the tzaddik, it is considered a demotion from his level, and hence is similar to the forbidden thoughts that a layperson struggles with.] This is the difference between humans and angels. Angels are not in a physical body and do not struggle from forbidden or foreign thoughts, while humans, even the greatest of them, will suffer from forbidden or foreign thoughts due to the body. [In this light, it is recorded in the letter of the Rebbe Rayatz that when Moshe teaches Parshas Lech Licha to the little children in heaven he explains that even Avraham had foreign thoughts as he doubted G-d’s promise, and so too it is recorded in a story with the Maggid that he doubted or questioned his master the Besht.^[1]]

[1] See also Koveitz Michtavim Ohalei Yosef Yitzchak Tehillim p. 197-198