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.
"When a person dies, his works end, except for three: ongoing charity, knowledge that is benefited from, and a righteous child who prays for him."
Prophet Mohammed (PBUH)
"The best of what a man leaves behind are three: a righteous child who supplicates for him, ongoing charity the reward of which reaches him, and knowledge that is acted upon after him."
Sunan Ibn Mājah
"Every day two angels come down from Heaven and one of them says, 'O Allah! Compensate every person who spends in Your Cause,' and the other (angel) says, 'O Allah! Destroy every miser.'"
Sahih Bukhari