Fath al-Rabbani

Benefits: … It is understood from this that providing iftar (meal to break the fast) to a fasting person is also an extremely blessed and virtuous act. The author has not mentioned any specific supplication (dua) for iftar; its details are as follows: Iftar should be done by saying "Bismillah" (In the name of Allah), as is evident from the hadiths regarding the etiquettes of eating. Then, after breaking the fast, the following supplications should be recited: It is narrated from Sayyiduna Abdullah ibn Umar radi Allahu anhuma, he says: Whenever the Prophet sallallahu alayhi wa sallam broke his fast, he would say: "Dhahaba al-zama'u wabtallat al-urooqu wa thabata al-ajru in sha Allah." (The thirst has gone, the veins are moistened, and the reward is established, if Allah wills.) (Abu Dawud, Nasa'i)

Sayyiduna Abdullah ibn Zubair radi Allahu anhu says: The Messenger of Allah sallallahu alayhi wa sallam broke his fast at the house of Sayyiduna Sa'd ibn Mu'adh radi Allahu anhu and made this supplication: "Aftara 'indakumu al-sa'imoon, wa akala ta'amakumu al-abraar, wa sallat 'alaykumu al-mala'ikah." (May the fasting people break their fast with you, may the righteous eat your food, and may the angels send blessings upon you.) (Abu Dawud, Ibn Majah)

The commonly known supplication among the general public, "Allahumma laka sumtu …" is found to be weak in all its chains of transmission.