What is the constitutional basis of state immunity from suit?

The immunity of the State from suit, known also as the doctrine of sovereign immunity or non-suability of the State, is expressly provided in Article XVI of the 1987 Constitution, viz:

Section 3. The State may not be sued without its consent. 

(Air Transportation Office vs. Sps. Ramos, G.R. No. 159402, February 23, 2011)