can you mix multiple days pumped milk

KK

I was just wondering if it's safe to mix milk from two different days. I pumped some yesterday and some today, is it safe to put both days milk in a bottle at the same time to feed to my little guy if needed?

edit: I don't mean mix days as I'm pumping/storing. I mean when I am preparing a bottle for him can I mix two days worth of pumped milk?