Sayyiduna Ibn Abbas and Sayyidah Aishah (may Allah be pleased with them) both narrated that the Messenger of Allah (peace and blessings be upon him) entered the mosque, and the voices of the people reciting the Qur'an were like the humming of bees. He (peace and blessings be upon him) said: "Islam will spread, then there will be a period of slackness in it; whoever's slackness inclines towards extremism and innovation, they are the people of Hell."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10730