Mishnà su Esodo 22:28

He who gives terumah before first-fruits, or first tithe before terumah, or second tithe before first tithe, although he transgresses a negative commandment, that which he has done is done, for it is said: “You shall not delaying the skimming of the first yield of your vats” (Exodus 22:28).

If one was taking terumah from a cistern and said: "Let this be terumah provided it comes up safely," [it is implied that he meant] safely from being broken or spilled, but not from becoming impure; But Rabbi Shimon says: also from impurity. If it were broken, it does not render [the contents of the cistern] subject to the restrictions of terumah. How far away can it be broken and still not make [the contents of the cistern] subject to terumah restrictions? Only so far that if it rolls back, it can reach the cistern. Rabbi Yose says: even if one had the intention of making such a stipulation, but did not do so, and it broke, it does not make the [contents of the cistern] subject to terumah restrictions, for this is a stipulation laid down by the court.