La Genèse 42:18 Midrash : Midrash Tanchuma, Midrash Tanchuma Buber, Mekhilta DeRabbi Yishmael & Devarim Rabbah

(Numb. 30:3:) “When someone makes a vow (neder) to the Lord.” Let our master instruct us: How are konamot (i.e., vows of abstinence) and vows (nedarim)? Thus have our masters taught (in Ned. 2:1): [If one makes] a konam (i.e., a vow of absitinence) [that he will not sleep, that he will not speak; [if he utters a konam to his wife] “that I will not have marital relations with you,” such a one is liable to [the injunction] (in Numb. 30:3), “he shall not break his word.” [If he swears] an oath (shevu'ah)] that he will not sleep, that he will not walk, he is forbidden [to do so].¹Cf. Ned. 2:2-5; Ned. 13b, 14b-15a; 20a; yNed. 2:2-5 (37b-6); above, Lev. 1:16. Oaths (shevu'ot) carry more weight than vows (nedarim); and vows, than oaths. How so? [if one makes] a konam not to make a sukkah, not to take up a lulab, not to put on phylacteries, in the case of vows (nedarim) it is forbidden to put them on or to make them, even though they are commandments (of the Torah); but in the case of oaths (shevu'ot) it is permitted, because one does not swear to transgress against the commandments. The Holy One, blessed be He, said to Israel, “Be circumspect with your vows (nedarim) and do not break them; for all who break vows (nedarim) end up in being faithless in oaths (shevu'ot).” And the one who is faithless in oaths is denying the Holy One, blessed be He through it and will never have forgiveness, as stated (in Exod. 20:7 = Deut. 5:11), “for the Lord will not exonerate [one who takes His name in vain].” [Yet] it is also written (in Jer. 4:2), “And you shall swear, ‘As the Lord lives,’ [in truth, in justice, and in righteousness].” The Holy One, blessed be He, said to Israel, “Do not think that you have permission to swear in My name even in truth.²Numb. R. 22:1. You are not entitled to swear by My name unless you possess all the following attributes (of Deut. 10:20), “The Lord your God you shall fear, Him you shall serve, to Him you shall hold fast, [and by Him you shall swear]”: That you should be like those three who were called God-fearing, Abraham, Job, and Joseph: Abraham of whom it is written (in Gen. 22:12), “For now I know that you fear [God].” Concerning Job it is written (in Job 1:1), “the man was blameless [and upright, one who feared God].” Concerning Joseph it is written (in Gen. 42:18), “for I fear God.” Ergo (in Deut. 10:20), “The Lord your God you shall fear.” (Deut. 10:20, cont.:) “Him you shall serve.” [You do so,] if you turn [all] your attention to the Torah, fulfill [its] commandments and have no other work (abodah). It therefore is stated (ibid.), “Him you shall serve (rt.: 'bd).” (Deut. 10:20, cont.:) “To Him you shall hold fast.” Can one hold fast to the Divine Presence? Moreover, has it not already been stated (in Deut. 4:24), “For the Lord your God is a consuming fire?” It is simply [being stated with reference to] anyone marrying off his daughter to a scholar who reads [Scripture] and recites [Mishnah], that he engage in commerce³Gk.: pragmateia. for him and have him benefit from his assets.⁴Ket. 111b; cf. Sot. 14a. It is with reference to [such a] one that it is stated (in Deut. 10:20), “to him you shall hold fast.”
If you have all these [attributes] you may swear; if not, you are not entitled to swear. There is a story about King [Jannai], that he had two thousand towns and they all were destroyed because of a true oath. (Numbers 30:17:) “Between a man and his wife, between a father and his daughter.” Just like a man only annuls vows of self-affliction and matters between him and her, so too a father only annuls with regards to self-affliction and what is between him and her.

That you should be like those three who were called God-fearing, Abraham, Job, and Joseph:
Abraham of whom it is written (in Gen. 22:12): <FOR NOW I KNOW> THAT YOU FEAR GOD.
Concerning Job it is written (in Job 1:1): BLAMELESS AND UPRIGHT, ONE WHO FEARED GOD AND TURNED AWAY FROM EVIL.
Concerning Joseph it is written (in Gen. 42:18): FOR I FEAR GOD. Ergo (in Deut. 10:20):THE LORD YOUR GOD YOU SHALL FEAR.
[(Deut. 10:20, cont.:) HIM YOU SHALL SERVE.] <You do so,> if you turn <all> your attention to the Torah, fulfill <its> commandments and have no other work. It therefore is stated (ibid.): HIM YOU SHALL SERVE (rt.: 'BD).
(Deut. 10:20, cont.:) TO HIM YOU SHALL HOLD FAST. Can one hold fast to the Divine Presence? Moroever, has it not already been stated (in Deut. 4:24): FOR THE LORD YOUR GOD IS A CONSUMING FIRE? It is simply <being stated with reference to> anyone marrying off his daughter to a scholar, who reads <Scripture> and recites <Mishnah>, that he engage in commerce⁴Gk.: pragmateia. for him and have him benefit from his assets.⁵Ket. 111b; cf. Sot. 14a. It is with reference to <such a> one that it is stated (in Deut. 10:20): TO HIM YOU SHALL HOLD FAST.

In what lies in the other ark it is written (Exodus 20) "I am the L–rd your G–d," and of Joseph it is written (Genesis 50:19) "Am I in the place of G–d?" In what lies in this ark it is written (Exodus 20) "There shall not be before you any other gods," and of Joseph it is written (Genesis 42:18) "It is G–d whom I fear." (Exodus 20) "You shall not take the name of the L–rd your G–d in vain." And of Joseph it is written (Genesis 42:15) "By the life of Pharaoh," (Joseph not swearing by "the life" of the L–rd.) (Exodus 20) "Remember the Sabbath day." Joseph (Genesis 42:16) "slaughter an animal and prepare it," "prepare" alluding to Sabbath eve, it being written here "prepare," and elsewhere (Exodus 16:5) "And it shall be on the sixth day that they shall prepare." (Exodus 20) "Honor your father." Joseph (Genesis 37:13) "And Israel said to Joseph: Are your brothers not grazing (the sheep) in Shechem? Go, and I will send you to them. And he said to him: Here I am" (at your service). Joseph knew that his brothers hated him, but he would not transgress the words of his father. (Exodus 20) "You shall not kill." He did not kill Potiphar (even though he could have.) (Exodus 20) "You shall not commit adultery." He did not commit adultery with the wife of Potiphar. (Exodus 20) "You shall not steal." He did not rob Pharaoh, viz. (Genesis 47:14) "And Joseph collected all of the money, etc." (Exodus 20) "You shall not testify falsely against your neighbor." Joseph did not tell his father what his brothers had done to him. Now does this not follow a fortiori, viz.: If he did not testify (against them) even truthfully, how much more so, falsely! (Exodus 20) "You shall not covet." He did not covet Potiphar's wife. It is written (Leviticus 19:17) "Do not hate your brother in your heart." And of Joseph it is written (Genesis 50:21) "And he counseled them and he spoke to their hearts." It is written (Leviticus 19:18) "You shall not take revenge and you shall not bear a grudge," and (in respect to Joseph, Genesis 50:20) "And you contemplated evil against me, but G–d contemplated it for the good." (Leviticus 25:36) "And let your brother live with you." (Genesis 47:12) "And Joseph sustained his father and his brothers, etc."...