whether advocates should not have another source of income at all ?

EMployment is prohibited 

Section 49 of the Advocates Act, 1961 puts restriction on employment of an advocate

An advocate may not work full-time for any individual, government, corporation, or other entity. If the advocate chooses to work full-time, they must notify the State Bar Council on whose rolls they have been enrolled. As a result, the right to practice is lost.