my conscience will not permit me to take advantage of thy ignorance."
Baba Batra, 88a; Makkot, 24a; Rashi to Makkot, 1. c.; Sheiltet de-Rab Ahai Gaon, § 36 (ed. Venice, 1546, p. 14a); Isaac Aboab, Menorat Ha-Maor, part II, ch. I, § 46.
Reverence for Truth and Simplicity not to be Sacrificed to the Forms of Courtesy—A Lesson of Rabbi Saphra
It happened that Rabbi Saphra took a walk with his disciples. As they went along, they met, at some distance from the town, a learned man, who, supposing that the Rabbi came purposely to meet him, thanked him for his condescension. "Do not thank me." said Saphra, "I only came to take a walk." The man was disconcerted, and betrayed some confusion. The disciples, who witnessed what passed, asked their master why he acted thus. "Would you, then, have me guilty of a falsehood?" said the pious Rabbi. "Nay," rejoined his disciples, "but thou mightest have been silent." "My children," said the virtuous instructor, "it becomes not a son of Israel to assume a merit not due to him; nor to cause, either by words or their absence, a false impression upon the mind of a neighbor."
(See the references in the last chapter.)