Volume 4, Book 52, Number 287:
Narrated ‘Amr bin Maimun:
Umar (after he was stabbed), instructed (his would-be-successor) saying, “I urge him (i.e. the new
Caliph) to take care of those non-Muslims who are under the protection of Allah and His Apostle in
that he should observe the convention agreed upon with them, and fight on their behalf (to secure
their safety) and he should not over-tax them beyond their capability.”