Musnad Ahmad 937:9

Musa ibn Dawud narrated to us, Ibn Lahi'ah informed us, from Ibn Hubayrah, from Abu Tamim al-Jayshani, who said: I heard Abu Dharr saying: I was walking with the Prophet, may Allah bless him and grant him peace, one day toward his house, and I heard him say: "Other than the Dajjal, there is something more feared for my Ummah than the Dajjal." When I feared that he would enter, I said: "O Messenger of Allah, what thing is more feared for your Ummah than the Dajjal?" He said: "The misguided leaders."