From De Concordia:

Now, if something is going to occur without necessity, God foreknows this, since he foreknows all future events. And that which is foreknown by God is, necessarily, going to occur, as is foreknown. Therefore, it is necessary that something be going to occur without necessity. Hence, the foreknowledge from which necessity follows and the freedom of choice from which necessity is absent are here seen (for one who rightly understands it) to be not at all incompatible. For, on the one hand, it is necessary that what is foreknown by God be going to occur; and, on the other hand, God foreknows that something is going to occur without any necessity