By one fasting when presented with food and does not break his fast
All Duas
When you are invited (to eat) then reply to the invitation. If you are fasting then invoke Allah's blessings (on your host), and if you are not fasting then eat.
1
إذا دُعي أحدكم فليجب ، فإن كان صائماً فليصل وإن كان مفطراً فليطعم, ومعنى فليصل أي فليدع