Hadeeth

Abu Hurayah (RA) said: "I heard the Prophet (SAW) say: The first person to be judged on the Day of Resurrection will be a man who was martyred. He will be brought forth and Allah will remind him of His blessings and he will recognize them.
Then he will be asked, 'What did you do with them?'.
He will say 'I fought for Your sake until I was martyred.'
Allah will say 'You have lied. You only fought so that people would say ,'He is courageous and brave,' and they did say it.'
Then He will order that he be dragged on his face and thrown into the Fire.

Then there will be a man who studied much and taught others and recited the Quran. He will be brought forth and Allah will remind of His blessings and he will recognize them.
Then he will be asked, 'What did you do with them?'
He will say 'I studied much and taught others and recited the Quran for Your sake.'
Allah will say 'You have lied. You studied so that people would say 'He is a great scholar,' and you recited the Quran so that they would say 'He is a qaari,' and they did say it.'
Then He will order that he be dragged on his face and thrown into the Fire.

Then there will be a man to whom Allah gave all types of wealth in abundance. He will be brought forth and Allah will remind him of His blessings and he will recognize them.
Then he will be asked, 'What did you do with them?'
He will say 'I have never seen any way in which You would like money to be spent for Your sake without spending it.'
Allah will say 'You have lied. You did that so people would say 'He is generous' and they did say it.'
Then He will order that he be dragged on his face and thrown into the Fire. "


'O you who believe! Cancel not your charity by reminders of your generosity or by injury- like those who spend their substance to be seen of men, but believe neither in Allah nor the Last Day. They are in parable like a hard barren rock on which is a little soil, on it falls heavy rain which leave it a bare rock. They will able to do nothing with aught they have earned. And Allah guides not those who reject faith.' Quran 2: 264

To remind someone of the charity you have given him cancels out the reward of the charity just like pouring water washes away any trace of soil on the rock. A reminder to avoid boasting and to always serve Allah alone, and not do things for the sake of others or to be seen by others