Abd al-Rahman bin Hilal (may Allah have mercy on him) narrates: My father sent me to Sayyiduna Jarir bin Abdullah (may Allah be pleased with him) and said: Convey my salam to him and ask him: How did you hear the Prophet (peace and blessings be upon him) say: "Whoever introduces a good practice that is followed and acted upon"? He said: I came to him and asked him, and he said: "He will have a reward equal to the reward of every man who acts upon it, without anything being reduced from their rewards. And whoever introduces an evil practice that is followed and acted upon will bear a sin equal to the sin of every man who acts upon it, without anything being reduced from their sins."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2435