Musnad Ahmad 33:326

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Ibn Khuthaym, from 'Abd al-Rahman ibn Sabit, from Jabir ibn 'Abd Allah, that the Prophet, peace and blessings of Allah be upon him, said to Ka'b ibn 'Ujrah: "May Allah protect you from the leadership of the foolish." He said: "And what is the leadership of the foolish?" He said: "Leaders who will come after me, who do not follow my guidance and do not practice my Sunnah. Whoever believes their lies and assists them in their oppression, they are not of me, and I am not of them, and they shall not come to my Hawd (fount). And whoever does not believe their lies and does not assist them in their oppression, they are of me, and I am of them, and they shall come to my Hawd." "O Ka'b ibn 'Ujrah, fasting is a shield, charity extinguishes sin, and prayer is an offering—or he said: a proof." "O Ka'b ibn 'Ujrah, no flesh that grows from unlawful gain shall enter Paradise; the Fire is more fitting for it." "O Ka'b ibn 'Ujrah, people go out in the morning: one who sells his soul and sets it free, and one who sells his soul and ruins it."