TestnNG Error: No sourcedir was specified

Getting Error while trying to execute testNG Class from Command Line Argument on Windows.

Exception in thread "main" org.testng.TestNGException: No sourcedir was specified at org.testng.TestNG.checkConditions(TestNG.java:1170) at org.testng.TestNG.privateMain(TestNG.java:1010) at org.testng.TestNG.main(TestNG.java:997)