The Messenger of Allaah (salallaahu ‘alaihi wa sallam) said,
“Whoever feeds a fasting person will have a reward like that of the fasting person, without any reduction in his reward.”
[At-Tirmidhi, authenticated by Al-Albani (rahimahullaah).]
Shaykh Muhammad bin Saalih Al-‘Uthaimeen (rahimahullaah) said,
“Those who have the ability should strive to feed those who are fasting (when it’s time to break the fast) either in the masaajid or in other places. This is since whoever feeds a fasting person, he will receive the same reward as the one fasting. So if a person feeds his brothers who are fasting, he will receive the same reward as them. Therefore, those whom Allaah has granted wealth should take advantage of this opportunity to obtain a great reward.”
[48 Su’aalan fis-Siyaam]
The following are taken from Fortress of the Muslim, Dar-us-salam Publication
Offered food when fasting & you decline:
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.
Breaking fast in someone’s home:
أَفْطَرَ عِنْدَكُم الصّائِمونَ وَأَكَلَ طَعامَكُمُ الأبْرار، وَصَلَّتْ عَلَيْكُمُ الملائِكَة
Aftara ‘indakumus-saa’imoona, wa ‘akala ta’aamakumul-‘abraaru, wa sallat ‘alaykumul-malaa’ikatu
With you, those who are fasting have broken their fast, you have fed those who are righteous, and the angels recite their prayers upon you.
Abu Dawud 3/367, Ibn Majah 1/556, An-Nasa’i, ‘Amalul-Yawm wal-Laylah 296-8. Al-Albani graded it authentic in Sahih Abu Dawud 2/730