At the time of his blessed nikaah to Hazrat Khadijah (radhiyallahu ‘anha), Rasulullah (sallallahu ‘alaihi wasallam) was twenty-five years old whilst Hazrat Khadijah (radhiyallahu ‘anhu) was forty. The mahr (dowry) was fixed at twenty camels. However, according to Seerat Ibn Hishaam and Hafiz Abu Bishr Dawlaami (rahimahullah), the stipulated mahr (dowry) was twelve and a half ooqiyah of silver. Each ooqiyah is equivalent to forty dirhams. Hence, the total dowry was five hundred dirhams. This was the first nikaah of Rasulullah (sallallahu ‘alaihi wasallam) whilst it was Hazrat Khadijah’s (radhiyallahu ‘anha) third.
Insha Allah, we will discuss this in more detail in the chapter pertaining to the Azwaaj-e-Mutahharaat (the blessed wives of Rasulullah (sallallahu ‘alaihi wasallam).
(Extracted from Seeratul Mustafa 1/112)