There are his own words...

There are his own words: "When I was struggling against AL-AMIN and was in a precarious situation, the people of SISTAN and KIRMAN revolted. There was unrest in KHURASAN. My treasury was empty, so I could not rely on my soldiers whom I did not pay. In such perilous circumstances, I prayed to God, taking the oath that if overcame all those odds and acceded to the throne, I would hand the caliphate over to its real and rightful master, i.e. the most suitable among Imam Ali's descendants.