During their stay at the capital he very closely observed...

During their stay at the capital he very closely observed and noted their capabilities and eventually arrived at the conclusion that not one of them deserved to succeed him. He therefore spoke to them all in an assembly in 201 AH telling them in categorical terms that none of the `Abbasids deserved to succeed him.

He demanded allegiance to Imam ar-Rida from the people in this very meeting and declared that royal robes would be green in future, the colour which had the unique distinction of being that of the Imam'