He left his camel outside and went in with his prayer mat and spent several hours offering thanks to Allah, praying and promising that he’d be a good Muslim in the future, help the poor and be an upstanding pillar of his community.
When he emerged it was already dark and lo and behold – his camel was gone!
He immediately flew into a violent temper and shook his fist at the sky, yelling:
“You traitor, Allah! How could you do this to me? I put all my trust in you and then you go and stab me in the back like this!”
A passing sufi dervish heard the man yelling and chuckled to himself.
“Listen,” he said, “Trust God but, you know, tie up your camel.”
Source: The Essential Rumi from Coleman Barks