Do good for the sake of your Lord alone and never expect anything in return

In the Holy Quran we are told: 

     "(The righteous are those) who feed the poor, the orphan 
     and the captive for the love of Allah, saying: 'We feed you 
     for the sake of Allah alone, we seek from you neither 
     reward nor thanks.'" [Sura Al-Insan 76:8-9]

Who is 'Poor' on the Day of Judgement

Abu Hurairah related that Prophet Muhammad ﷺ (peace be upon him) asked:
          "Do you know who is poor?"
The companions answered: 'A poor person, in our opinion, is one who has no money.' But Rasulullah ﷺ (peace be upon him) said:
          "A poor person among my people is one who faces the Day of Judgment having performed the Salat, Zakat and Siyam but who had insulted someone, slandered someone, misused someone`s money, shed someone`s blood and beaten someone else. Each one of them shall be given some of his good deeds. Should he not have enough good deeds, then he will be given their sins. Then he will be thrown into Hell." (Muslim)