Conquest of Spain
According to the general books of Islamic history the conquest of Spain is attributed to Tariq b Ziyad and Musa b Naseer in 711 - 712 C.E. in the time of the Umayyad Caliph Walid b Abdul Malik. According to Tabari, Spain was conquered some sixty years earlier during the caliphate of Uthman.

Tabari's account
According to the account of Tabari, when North Africa had been duly conquered by Abdullah b Sa'ad b Abi Sarah, two of his Generals Abdullah b Nafiah b Husain, and Abdullah b Nafi' b Abdul Qais were commissioned to invade Spain by sea. On this occasion Uthman is reported to have addressed a letter to the invading force. In the course of the letter, Uthman said:

"Constantinople will be conquered from the side of Spain. Thus if you conquer Spain you will have the honor of taking the first step towards the conquest of Constantinople. You will have your reward in this behalf both in this world and the next."

Kaab al Ahbar, an eminent companion and a counselor of Uthman is reported to have said:

"The people who conquer Spain after crossing the sea will be identified on the Doomsday on account of the special light that would radiate from them."

Campaigns in Spain
No details of the campaigns in Spain during the caliphate of Uthman are given by Tabari or any other historian. The account of Tabari is merely to the effect that an Arab force aided by a Berber force landed in Spain, and succeeded in conquering it. We do not know where the Muslim force landed, what resistance they met, and what parts of Spain did they actually conquer. Anyhow it is clear that the Muslims did conquer some parts of Spain during the caliphate of Uthman. Presumably the Muslims established some colonies on the coastland of Spain. There are reasons to presume that these Muslims entered into trade relations with the rest of Spain and other parts of Europe.