On the last day of Ramadan in the year before the last year, I had a friend whose friend used to work in a fast food restaurant. My friend’s friend invited my friend to visit him at his work place; the restaurant. I went with my friend and, while we were there, my friend’s friend (who worked in the restaurant) gave my friend a bag full of sandwiches. My friend and I ate the sandwiches at iftar (meal with which you break your fast) time. The issue is that we did not pay for the food. When my friend’s friend gave the bag to my friend, the restaurant was very busy with customers, and he approached my friend as one of the waiting customers. The supervisor was not there. The workers at the restaurant did not notice this incident either. Is my fasting of that day valid? Do I have to observe expiation? If yes, how much should I pay?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

You should not have eaten these sandwiches if you knew that they were unrightfully given to your friend. You should rather have advised your friend against being involved in such an ugly conduct, especially in Ramadan. Since that incident has already taken place, you have to find a way to pay the restaurant back for what you ate. You must advise your friend to do the same as well. You both have to repent to Allaah for that sin. As for your fast, it is valid, and no expiation is due on any of you. You are only required to repent, seek Allaah's forgiveness, and pay back the restaurant's owner for the sandwiches. 

Allaah Knows best.