פירוש על עבודה זרה 48:6

Here the Jews offer as sacrifices cattle they took from the Philistines during a war. Again, this is proof that animals can be taken from non-Jews. Here, these are obviously non-Jews and obviously this was after the giving of the Torah. They resolve the difficulty by saying that it was a temporary ruling, in which the rules were suspended for the needs of that specific moment. They prove that this was indeed a temporary ruling by noting that these are female cattle, and normally female cattle cannot be used as burned offerings. Thus this must have been a special ruling.