Timbuktu is a city in the Western African nation of Mali.  It has a long history as a trading outpost, linking African, Arab, and Jewish traders.  Timbuktu was established by the nomadic Tuareg around the 10th century.  In the 11th century permanent settlements popped up in Tinbuktu.  In these settlements Islam and literature was introduced. 

"Timbuktu's long-lasting contribution to Islamic and world civilization is scholarship. Timbuktu is assumed to have had one of the first universities in the world. Local scholars and collectors still boast an impressive collection of ancient Greek texts from that era.  By the 14th century, important books were written and copied in Timbuktu, establishing the city as the centre of a significant written tradition in Africa."

How did the city of Timbuktu contribute to Islam?

Timbuktu is a city in the West African nation of Mali that has a long and fascinating history.  It began as a gathering point for rest and trade along the Niger river, but developed quickly from there.  Around 1200 A.D., Muslim scholars began to arrive in the city after the Ghana Empire was invaded, which forced them to flee.  They brought Islam to the area and solidified it there.

These scholars created Sankore University there, one of the first universities in the world, as well as some 180 Koranic schools.  Because of this early dedication to scholarship, it is estimated that today Timbuktu hosts some 100,000 ancient manuscripts that range in topic from Islam and science to law and daily life.  There may be as many as 300,000 in the region.

So that's it in a nutshell.  The major contribution that Timbuktu made to Islam is in the promotion of scholarship.