Birbal was famous . . . . . . . . his uncommon wit.

The correct preposition to use in this sentence is for. The sentence should read: "Birbal was famous for his uncommon wit." This construction indicates the reason for Birbal's fame, which is his uncommon wit.

The other options do not fit contextually:
A. "Birbal was famous at his uncommon wit." (Incorrect)
B. "Birbal was famous on his uncommon wit." (Incorrect)
D. "Birbal was famous with his uncommon wit." (Incorrect)