This excerpt from the writings of the great 10th-century muslim historian masoudi describes the seventh-century caliph abu bakr the truthful. use this excerpt to answer the following question:

during his rule he wore but a single linen garment and a cloak. in this simple dress he gave audience to the chiefs of the noblest arab tribes and to the kings of yemen. the latter appeared before him dressed in richest robes, covered with gold embroideries and wearing splendid crowns. but at sight of the caliph, shamed by his mingling of pious humility and earnest gravity, they followed his example and renounced their gorgeous attire.
—excerpt from the book of golden meadows by masoudi.

which additional source would provide the most accurate support for masoudi's description?

a. the complete text of masoudi's book
b. a 7th-century portrait of the caliph
c. a history book by a present-day professor
d. a text by a rival of masoudi from his own time