Sahih Muslim Book 34, Hadith Number 6466.

Chapter : Pertaining to one who introduced something good or evil or he who called to righteousness or to the path of error.

Jarir b. Abdullah reported that some desert Arabs clad in woollen clothes came to Allah’s Messenger (may peace be upon him). He saw them in sad plight as they had been hard pressed by need. He (the Holy Prophet) exhorted people to give charity, but they showed some reluctance until (signs) of anger could be seen on his face. Then a person from the Ansar came with a purse containing silver. Then came another person and then other persons followed them in succession until signs of happiness could be seen on his (sacred) face. Thereupon Allah’s Messenger (may peace be upon him) said: He who introduced some good practice in Islam which was followed after him (by people) he would be assured of reward like one who followed it, without their rewards being diminished in any respect. And he who introduced some evil practice in Islam which had been followed subsequently (by others), he would be required to bear the burden like that of one who followed this (evil practice) without their’s being diminished in any respect.