In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
The Prophet [sallal-laahu-alayhi-wasallam] said: He is not a (true) believer whose stomach is full while his neighbour is hungry”. [Ref 1]
This Hadeeth [clearly shows] that the one whose stomach is full while his neighbour is hungry is not a believer of complete Eemaan. A person of complete Eemaan is the one who checks on his neighbour if the neighbour is in need of him. It is not possible for a neighbour to be enjoying himself with foods and drinks while his [other] neighbour cannot find anything and he does not give him anything. This [behaviour] does not reflect the manners of a believer with complete Eemaan. And because of this-in this hadeeth- the Prophet [sallal-laahu-alayhi-wasallam] negated the completeness [of the Eemaan of the one who behaves in such a manner]; rather a believer of complete Eemaan is the one who is generous to his neighbour as much as he is able, especially when in need of a necessity such as food and drink. [Ref 2]
[Ref1: Reported by Imaam Al-Bukhaari (rahimahullaah) in Adabul Mufrad Number 112 & declared authentic by Imaam Albaani (rahimahullaah) in his checking of Adabul Mufrad page 50. Publisher Daar As-Siddeeq 2nd ed [1421 AH/ Year 2000]; [Ref 2: An Excerpt from Awnul Ahadis Samad Sharhul Adabul Mufrad’ page137, Vol 1- by Shaikh Zayd Bin Haadi Al-Madkhali (rahimahullaah). Slightly paraphrased]