Anas radiallahu anhu relates: "When Rasulullah sallallahu alayhe wasallam intended to write letters to the kings of 'Ajam (non arabs), inviting them to Islam, the people said that they did not accept letters without a seal (stamp) on them. Rasulullah sallallahu alayhe wasallam therefore had a ring made, the whiteness of which is still before my eyes."