When a family hosted the Prophet ﷺ for a meal, he thanked them with a du'a for blessing, forgiveness and mercy. If you are invited while fasting, accept, and make du'a for your hosts instead of eating (Sahih Muslim 1431).
Allahumma barik lahum fima razaqtahum, waghfir lahum warhamhum.
“O Allah, bless them in what You have provided for them, forgive them and have mercy on them.”
The Prophet ﷺ made this du'a for a family that hosted him for a meal.
Allahumma at'im man at'amani, wa asqi man asqani.
“O Allah, feed the one who fed me, and give drink to the one who gave me drink.”
Al-Miqdad reported that the Prophet ﷺ raised his head to the sky and said this on a night his share of milk had been drunk. It suits anyone who hosts you, including the one who gives you iftar.
Aftara 'indakumus-sa'imun, wa akala ta'amakumul-abrar, wa sallat 'alaykumul-mala'ikah.
“May those who fast break their fast with you, may the righteous eat your food, and may the angels pray for you.”
Said to the hosts after eating at their home, especially at iftar.