"When I die," the laborer said, "wash for me the woolen robe and wrap that I have on, and sell my shovel. That'll be enough [for my burial clothes and the price of my interment]. But the robe has a pocket, and when you undo the seam you'll find a ring. Take the ring and await the day the caliph Harun al-Rashid rides by. On that day, you must make yourself conspicuous. Call out to him, and show him the ring, and surrender it to him when he bids you approach. But none of this until I'm dead and buried."
I agreed to his terms, and after he died I carried out all his instructions. Then I waited for the caliph to appear. When that day came, I staked out a place along his route, and as he rode by I shouted, "Commander of the Faithful! I am entrusted with something that belongs to you," and flashed the ring at him. At his command, I was seized and borne along to the palace, where he sent away every one of his guardians and retainers and asked my name. "‘Abd Allah ibn al-Faraj," I said.
"Where did you get this ring?" he asked. I told him my story of the young man, and the caliph burst into tears that moved me to pity. I waited for him to take notice of me again, and then I asked, "What relation was he to the Commander of the Faithful?"
"He was my son," the caliph said. I asked him, "How did he get into this condition?"
"He was born to me before I became caliph," Harun said. "He grew up strong and healthy, and studied Qur'an and religious science, but when the Caliphate was thrust on me, he fled, taking with him no reminder of the world around me. He never lost reverence for his mother, though, and I pressed this ring on her, a ruby ring of great price, and told her: 'Give this to him, and ask him to keep it handy. Perhaps it will be of use in his hour of need.'
"After that," he continued, "his mother died, and from that time to this I know nothing about him but what what you've told me." Then he said, "Take me to his grave after night falls."
Night fell, and he came out alone with me from the palace, and walked until we were at the grave. The caliph sat down and wept strenuously until the dawn. When the sky began to lighten, we rose and returned to the palace, where he set a date with me to visit the grave again after a number of days. And I returned with him on the appointed night, and escorted him back to the palace afterward.
‘Abd Allah ibn al-Faraj said: I had no idea that he was Harun al-Rashid's son, until the caliph told me so himself.
So goes Ibn Abi 'l-Tayyib's version—a fine report, in my estimation, though the first version is better authenticated, with an unbroken chain of transmission by trustworthy narrators.
Popular storytellers have lengthened this account into an episodic tale. In their version, Ahmad is Harun's son by Zubayda [rather than the secret marriage of Harun's youth. This is how they say Ahmad turned his back on palace life and became an ascetic:] He went out hunting, only to encounter Salih al-Murri and hear him preaching, and then Ahmad's horse stumbled, and fell to the ground... But all of that is drivel. I report only what has been authenticated, and God gets the final say.
From Characters of Integrity by Ibn al-Jawzi; cf. the Book of Strangers
of al-Ajurri