DUBAI, May 5 (Reuters) - Mubadala Investment Company, Abu Dhabi's second biggest sovereign wealth fund, has sold its 7.6% stake in Abu Dhabi Islamic Bank to a unit of investment firm National Holding, they said in a joint statement on Friday.

Emirates International Investment Company (EIIC), the strategic investment arm of Abu Dhabi-based National Holding, was already ADIB's top shareholder and the acquisition of Mubadala's stake takes its holding to 47% of ADIB.

The transaction signalled "strong confidence in the prospects for long-term growth of the UAE's second largest Islamic lender by assets," the statement said.

It was "in line with Mubadala's strategy to create long-term value by optimizing a global portfolio of investments across a variety of sectors," the statement said, adding the state investor remained committed to the UAE's banking sector.

ADIB's first-quarter net profit jumped by more than half from a year earlier to 1.1 billion dirhams ($300 million). Its stock is up more than 16% so far this year, according to Refinitiv data.

Its market capitalisation is about $10.3 billion, Refinitiv data showed. At ADIB's current share price, Mubadala's 7.6% stake was worth more than $780 million, according to Reuters calculations.

Mubadala and EIIC did not disclose a value for the transaction in the statement.

($1 = 3.6719 UAE dirham) (Reporting by Yousef Saba Editing by Mark Potter)