It was narrated that Zayd ibn Khaalid al-Juhani said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Whoever gives iftaar to one who is fasting will have a reward like his, without that detracting from the reward of the fasting person in the slightest.”
Narrated by al-Tirmidhi, 807; Ibn Maajah, 1746. Classed as saheeh by Ibn Hibaan, 8/216 and by al-Albaani in Saheeh al-Jaami, 6415.
Shaykh al-Islam [Ibn Taymiyah] said: What is meant by giving him iftaar is giving him enough to satisfy him. Al-Ikhtiyaaraat, p. 194
Miftaahul-Ilm - Key to Knowledge 