And, despite everything, one has given a charity, then Satan tries his level best to render the good deed null and void and thus the person doesn't qualify to get Reward for the good turn. To achieve this end, Satan would use all his skills to persuade the person to publicly brag about his charitable act. For example, Satan will put in the mind of the person to tell to the beneficiary of the charity, ' It was I who came to your rescue in time of need! None else would have helped you!' Or Satan would make him belittle the receiver of the charity by saying, ' Take this money now. But please don't come to me for help again!"

Therefore, Allah categorically says in the Holy Quran:

La tabtalu sadaqatekum bilmanne wal aaza

Render not your charities worthless by obligation and injuries (laid on them)- Al Baqarah 264

In a nutshell, Satan is a mortal enemy of men and always schemes to make their good turns go in vain. Therefore, they too have to render Satan's mean efforts ineffective!