Explanation:
cUthmān b. cAffān was the the third successor of the Prophet (S.A.W.) born in the year 573 C.E.( Introduction)
*The title Dhū-Nūrayn means the possessor of two lights.
*This title was given based on his close relationship with the Prophet (S.A.W.)
*The closeness was such that the Prophet (S.A.W.) gave him his daughter Ruqayyah in marriage.
*He and his wife Ruqayyah were among the first batch of Muslims to migrate to Abyssinia.
*On their return to Makkah, Ruqayyah died.
*cUthmān decided not to re-marry after the death of Ruqayyah.
*This is because he could not take anyone else as a father- in-law after the Prophet (S.A.W.)
*The Prophet (S.A.W.) loved him so much that he gave him another daughter Ummu Kulthūm in marriage.
*This was in the third year of Hijrah.
*Ummu Kulthūm too died in the fourth year of Hijrah.
*The holy Prophet (S.A.W.) expressed his admiration for his conduct after the death of his second wife.
*As a result he remarked that, if he had another unmarried daughter, he would have married her to him.
*His marriage with two daughters of the Prophet (S.A.W.) earned him the honorific title Dhū-Nūrayn.