How great is to feed a hungry person, however, it is greater to feed a fasting person.

It is not necessarily to feed a poor fasting person, as the Prophet indicated the plentiful reward of this sunnah regardless of the state of the fasting person.
Zaid ibn Khalid Al-Juhani reported: The Messenger of Allah, peace and blessings be upon him, said, “Whoever feeds a person who is breaking his fast will earn the same reward as him without anything being lessened from the reward of the fasting person.”
Source: Sunan At-Tirmidhi 807
Grade: Sahih (authentic) according to At-Tirmidhi

What is the reward of the fasting person, as we will be rewarded the same for feeding such fasting person to break his fast. In this concern, Abu Sa'id Al-Khudri (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) said, "Every slave of Allah who observes Saum (fasting) for a day in the Cause of Allah, Allah will keep his face from Hell-fire at a distance of seventy years."
[Al- Bukhari and Muslim].

Few pounds you spend to feed a fasting person would keep your face from hell-fire at the distance of seventy years.

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