Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "Whoever calls to guidance and that (guidance) is then followed, he receives a reward like the reward of those people, without anything being reduced from their reward; and whoever calls to misguidance, he bears a sin like the sin of those people, without anything being reduced from their sin."
Al-Tabarani recorded it in al-Mu'jam al-Kabir; its chain contains Ubaydullah bin Tammam, whom Imam Bukhari (may Allah have mercy on him) and a group (of scholars) declared da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب العلم / 773