There are two views regarding it. As for us, he has sworn regarding that which he cannot perform in its entirety, so his oath covered part of it in isolation, just like a generic noun.

Section (6): If he swears, "I will not drink from the Euphrates," and he drinks from its water, he breaks his oath, whether he drinks directly from it with his mouth [kara'a] or scoops from it and then drinks. This is the position of al-Shafi'i, Abu Yusuf, and Muhammad. Abu Hanifa said: He does not break his oath until he drinks directly from it, because the reality of that is drinking directly [al-kar'], so he does not break his oath by other than it, just as if he had sworn, "I will not drink from this vessel," then he poured from it into another and drank. Our argument is that the meaning of his oath is that he will not drink from the water of the Euphrates, because drinking usually occurs from its water, not from it itself, according to common usage [urf], so the oath is interpreted accordingly, just as if he had sworn, "I will not drink from this well," "I will not eat from this tree," or "I will not drink from this sheep." This differs from the cup because drinking from it is customary; for it is an instrument for drinking, unlike the river. What they mentioned is invalidated by the case of the well, the sheep, and the tree, and they have conceded that if he draws water from the well, or milks the ewe, or gathers from the tree, and drinks or eats, he breaks his oath; thus, it is the same in our case.

Section: If he swears that he will not drink from the water of the Euphrates, and he drinks from a river that draws from it, he breaks his oath because he is taking from the water of the Euphrates. If he swears that he will not drink from the Euphrates, and he drinks from a river that draws from it, there are two views. One of them is that he breaks his oath because the meaning of drinking from it is drinking from its water, so he breaks his oath, just as if he had sworn, "I will not drink from its water." This is one of the two possibilities for the companions of al-Shafi'i. The second is that he does not break his oath. This is the opinion of Abu Hanifa and his companions, except for Abu Yusuf, for there is a narration from him that he does break his oath. We have stated that he does not break his oath because what the river takes is attributed to that river, not to the Euphrates, and by attributing it to the river, it ceases to be attributed to the Euphrates, so he does not break his oath by it, like any other than the Euphrates.