Ibrahim ibn Abi al-Abbas narrated to us, Abdul Rahman ibn Abi al-Zinad narrated to us, from Amr ibn Abi Amr, from Asim ibn Umar al-Zhafari, from Mahmood ibn Labid, that the Messenger of Allah, peace and blessings be upon him, said: "Indeed, the thing I fear most for you..." and he mentioned its meaning.
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 23631