The intense slandering with respect to Imam Musa Ibn Ja’far (a.s) that reached the ears of Haroon al-Rashid, the Abbasid caliph, provoked him to say: ‘Present before me someone from the descendants of Abu Talib so that I can become aware of his (a.s) activities.’
Haroon’s minister, Yahya Barmaki, and some others suggested the name of ‘Ali Ibn Ismail – the Imam’s (a.s) nephew.
Upon Haroon’s orders, a letter was dispatched to him asking him to present himself before the Caliph in Baghdad. When the Imam (a.s) came to know of this, he called for him and questioned: “Where do you intend to go?”
‘Ali Ibn Ismail answered: “Baghdad.”
The Imam (a.s) inquired: “For what purpose?”
He replied: “I am burdened by great debts.”
The Imam (a.s) said: “I shall repay your debts and arrange for your expenses”, however ‘Ali Ibn Ismail refused the offer and instead, said: “Advise me!”
The Imam (a.s) said: “I advise you that you do not associate yourself in shedding my blood and do not make my children fatherless.” Repeating this three times, he (a.s) presented him with three hundred dinars and four thousand dirhams.
Later, when Ismail had left, he (a.s) said to those around him: “His slandering and vilification shall contribute to my murder.”10
Arriving in Baghdad ‘Ali Ibn Ismail went to Yahya Ibn Khalid Barmaki. That night Yahya said to him: “Tomorrow, in the presence of the Caliph, when you are questioned about Musa Ibn Ja’far (a.s), you must say: ‘I have never witnessed two caliphs exercising authority at one time – you, in Baghdad and Musa Ibn Ja’far (a.s), in Madinah. He is about to incite the people into rebelling against you!!’”
The next morning, arriving in the presence of the caliph, ‘Ali Ibn Ismail maligned and slandered the Imam (a.s) as much as he could. In the course of his talks he even said that people from distant places brought money for him and armed him with weapons, and that he was taking the pledge of allegiance from the people and intended to establish a separate state and government.
Hearing this, Haroon appeared to have been jolted out of sleep; he dismissed him from his presence and sent a sum of four thousand dirhams (or twenty thousand dirhams according to another report) for him to the place where he had been staying.
When the money was brought before him, an intense pain rose up inside his throat and he died then and there – a consequence of having severed the bond of kinship with his uncle – Musa Ibn Ja’far (a.s).
The bags of money were carried back to Haroon’s coffers while sorrow and regret was the only thing that Ismail carried to his grave.” ( Jame’ al-Nurain, pg. 24 )