Can I reuse breast milk if not finish during First feeding?

Xia

I’ve breast feed before but I never pumped and stored like I did with this baby. I thawed a 2 oz bag and he drank 1 oz and there’s another 1oz left. Can I save it for next feed? How long does it last out for if I can? Do I put it back in the fridge? Or do I just toss it. Thank you ladies.