The dua by one fasting, when presented with food and does not break his fast, is a simple sunnah helping us improve our Ikhlaq (good character). This dua is a simple little sunnah for the one fasting to invoke blessings upon one who offers food to them.
There are several authentic hadiths where this simple sunnah is narrated that every Muslim should keep in mind while fasting. In Sahih Muslim, Abu Huraira (رَضِيَ ٱللَّٰهُ عَنْهُ) reported Allah's Messenger (ﷺ) as saying, “If any one of you is invited, he should accept (the invitation). In case he is fasting, he should pray (in order to bless the occupants of the house), and if he is not fasting, he should eat. (Sahih Muslim 1431) This is reported again in Sunan Abi Dawud 2460. It is referenced again in Bulugh al-Maram Book 8, Hadith 1052.
Food & Drink Duas
This dua is a simple etiquette making up the Ikhlaq (good character) and amiable behavior of a Muslim. It is a Sunnah, the model behavior of Prophet Muhammad (ﷺ) preserved in tradition through authentic hadiths.
The benefit of following this sunnah is character development according to the Islamic values taught to us by Prophet Muhammad (ﷺ). A good Muslim should show gratitude for someone’s kindness by invoking blessings from Allah (سُبْحَانَهُ وَتَعَالَى) upon them.