What is world largest Muslim country according to area?

That depends what you mean by largest:

The nations with the highest percentage of the citizensbeing Muslim are

• Saudia Arabia and the Maldives (both at 100%).

The nations with the highest number of Muslims are

• Indonesia (197 million Muslims) and
• Pakistan (168 million Muslims)

The largest land area nations with a Muslim majority are

• Sudan (2.5 million km2)
• Algeria (2.38 million km2)
• Indonesia (1.92 million km2)