Musnad Ahmad 30:2038

Sulayman ibn Dawud al-Hashimi narrated to us, he said: Isma'il—meaning Ibn Ja'far—narrated to us, he said: Al-'Ala' informed us, from his father, from Abu Hurayrah, that the Prophet, may Allah bless him and grant him peace, said: "Whoever calls to guidance, there shall be for him of the reward like the rewards of those who follow him, without that diminishing anything from their rewards. And whoever calls to misguidance, there shall be upon him of the sin like the sins of those who follow him, without that diminishing anything from their sins."