Is a miser one who withholds his influence from benefiting people? And what is the authenticity of this Hadith?

We have not come across a Hadith (definition) with the exact wording mentioned. However, it is authentically reported from the Prophet (peace be upon him) that he encouraged striving to benefit people. Among these are his sayings (peace be upon him): "Whoever fulfills the needs of his brother, Allah will fulfill his needs," and "Allah helps the servant as long as the servant helps his brother," and "Whoever can benefit his brother, let him do so." He also encouraged intercession by saying: "Intercede, and you will be rewarded." He clarified that the most beloved of people to Allah are those most beneficial to people, and that walking with one's brother to fulfill his need is more beloved to him than secluding oneself for a month (in i'tikaf).