Musnad Ahmed: Hadith 2750

"Two believers met at the gate of Paradise, a rich believer and a poor believer, who had been in this world. The poor man was admitted to Paradise and the rich man was detained for as long as Allah willed, then he was admitted to Paradise, where he met the poor man who said: O my brother, what kept you? By Allah, you were detained so long that I feared for you. He said: O my brother, I was detained after you (moved on) in a terrible, harsh way, and I could not reach you until I sweated so much that if a thousand camels who had all eaten a bitter plant drank it, they would be able to quench their thirst from that sweat.