Responsa על משלי 23:1

Regarding the fourth matter, they responded: We have learned in a Mishnah (Shabbat 16:6): "A non-Jew who comes to extinguish a fire on Shabbat is neither told to extinguish not not to extinguish." To avoid monetary loss, the sage instructed that they should not be prevented from extinguishing a fire. This is similar to this shepherd who milks and curdles on his own accord, we have no obligation to prevent him from doing so, on account of monetary loss and the suffering of the animals. You could argue that it is similar to that which was taught (Shabbat 16:8): "If a non-Jew lights a lamp, a Jew may benefit from the light. But if it was lit for the Jew, they may not benefit from it. If the non-Jew draws water for his own animal, a Jew may have his animal drink from it. If it was drawn for the Jew, this is forbidden." It would seem from this that the results of labour done by non-Jews are forbidden for Jews when done for their sake, even if it was not asked for. Similarly, the shepherd milks and curdles for the Jew, how then should it be permitted? "Consider well what is before you." (Proverbs 23:1) For when it was taught that the results of actions done for the sake of Jews are forbidden, they are only forbidden for that same day: the animal is forbidden to drink from the water filled for it until the night after Shabbat. So too with the shepherd who milks and curdles - certainly, the milk is forbidden on Shabbat itself, but after Shabbat it becomes permitted. However, in the case of a Jew who bought the yearly milk supply of a non-Jew's flock, then anything the non-Jew added would now be done for the Jew - it is forbidden to keep these cheeses and milk produced on Shabbat. For we know the tale (Shabbat 139b:8) of one scholar who went to sleep on a ferry, and thus crossed the river and inspected the fruits of his orchard, while claiming that he just intended to sleep. We ruled there that a Torah scholar who will not come to transgress biblical violations of Shabbat is allowed to use such tricks to get around rabbinic prohibitions. From this we learn that common people are not.