The congregational supplication after having food mentioned above is baseless as far as the Purified Shar` (Law) is concerned. Thus, it is obligatory to abstain from this act, as it is considered a Bid`ah (innovation in religion). We should adhere to the Du`a' mentioned in the Sunnah, namely, to invoke Allah to bestow His blessing upon the inviter, and to perform such Du`a' individually. According to the Sunnah, one might say:
O Allah! Bless their livelihood, forgive them, and have mercy over them.
One may also say,
May the fasting people break their fast with you [by providing them food], may the pious people eat your food, and may the angels invoke blessings on you.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.