Emperor Musa went on hajj in 1324, and on his hajj he visited Cairo before continuing on to Mecca. He was not the first Malian monarch to make this hajj, nor was he the last. But, by the vagaries of fate, he is remembered for the particular wealth he brought with him on his pilgrimage.

Our earliest source describing this hajj comes from the syrian scholar Shihab al Umari, who wrote his account twelve years after the fact, based on interviews with people in Cairo who interacted with the Malian monarch. Here is an excerpt from al-Umaris account which concerns the extent of the mansa's wealth, and details his visit to the Mameluke sultan in Cairo. Since al-Umari's account is second hand and comes years after the event it relates, we should keep in mind the possibility that the story was embellished in the intervening years.

In this period, Italian city states like Venice were engaged in trade with Mameluke Egypt. These merchants would have heard the tale of the mansa's immense wealth, and spread the rumor to European ports on the Mediterranean shore. Emperor Musa holding a gold nugget is first depicted on the Catalan Atlas, which was produced in 1375, some fifty years after the hajj and 38 years after al-Umaris account.

I don't know of any scholarship or numismatics that has tried to directly link gold that ended up in Europe as the gold that came from Mali in 1324. Again, he wasn't the only one to bring gold. In fact, Arab sources make particular note of the wealth in gold of the monarchs of Ghana in the 9th-11th centuries, and mention other Malian monarchs bringing caravans of gold with them.

Rather, the mere rumor of immense wealth in a far off land was enough for Mansa Musa and Timbuktu to be remembered in Europe.