Translation:Shulchan Aruch/Orach Chaim/156
156: The order of conducting commerce. Contains 1 se'if.
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Afterwards, he should go to his businesses because any Torah that does not have work with it will end up becoming null and causes sin because the poverty will turn him away from the knowledge of his Creator. And nevertheless, he should not make his work the main thing but transient, and his Torah fixed, and both will be sustained in his hand. And he should do business with honesty and be careful not to mention the name of Heaven in vain, because wherever the mention of the name of Heaven is present, death is present. And he should be careful not to take an oath, even in truth, because 1,000 cities belonged to King Yannai and all of them were destroyed because they took oaths, even though they kept them. And he should be careful from partnering with heathens, for perhaps he will be obligated to take an oath and he violates "should not be heard on your mouth."
Gloss: And some are lenient with partnering with heathens these times because the heathens these times do not take an oath by idols. And even though they mention the idol, nevertheless their intention is to the Creator of heaven and earth, except that they associate the name of Heaven with something else. And we do not find that there is in this a violation of "Before a blind person you shall not place a stumbling block," because they are not given the prohibition of a composite godhead. [Ra"n - end of the first chapter of Avodah Zarah; and Rabbeinu Yerucham - netiv 17, chelek 5; and Tosafot - beginning of the first chapter of Bechorot]. And to do business with them without partnering, is permitted according to all, except on the day of their festivals. (Hagahot Maimoni - first chapter of the Laws of Idol Worship). And see Yoreh Deah, Laws of Idol Worship, chapter 147.