Pesachim 8B

הרי זה צדיק גמור! דילמא בתר דבדק אתי לעיוני בתרה.

this person is a full-fledged righteous person as far as that mitzva is concerned? These ulterior motives, e.g., seeking a reward, do not detract from the value of the mitzva. The Talmud answers: There is still concern lest he look for the needle after he searched for leaven and completed the search. There is danger that since he already completed the mitzva, its merit will not protect him when he is searching for the needle.

רב נחמן בר יצחק אמר: משום סכנת הגוים, ופלימו היא. דתניא: חור שבין יהודי לארמאי ⁠— בודק עד מקום שידו מגעת, והשאר מבטלו בלבו. פלימו אמר: כל עצמו אינו בודק מפני הסכנה.

Rav Naḥman bar Yitzḥak said: The danger referred to by the Tosefta is the danger posed by non-Jews. And this ruling is in accordance with the opinion of the tanna Pelimu. As it was taught in a baraita: With regard to a hole in a wall located between the residences of a Jew and a non-Jew, one searches in the hole as far as his hand reaches, and the rest he renders null and void in his heart. Pelimu said: One does not search the entire hole at all, due to the danger involved.

מאי סכנה, אי נימא סכנת כשפים, כי אישתמיש היכי אישתמיש? התם כי אישתמיש ⁠— יממא ונהורא, ולא מסיק אדעתיה. הכא ⁠— ליליא ושרגא הוא, ומסיק אדעתיה.

The Talmud asks: Due to what danger? If we say it is due to the danger of sorcery, i.e., the non-Jew will suspect the Jew of casting spells on him and will come to hate him and threaten him, if so, when he made use of the hole in the first place, how did he make use of it without arousing the enmity of his non-Jew neighbor? If the hole is never used there is no need to search it in any case. The Talmud answers: There, when he made use of the hole, it was during the day and there was light, and the non-Jew would not raise the suspicion that the Jew was casting spells in his mind. Here, it is during the night and the search is performed with a lamp, and the non-Jew would raise the suspicion that the Jew was casting spells in his mind.