The inscription on the reverse can be roughly translated as follow:
Perseverance, ascese, endurance salutations, these are the best for the state of nirvana, said the Buddha. If the monks do harm to others, these are not acts of vertu, don't accumulate bad thoughts, but accumulate the fruits of vertu! Discipline your own thoughts, that's the teaching of the Buddha. If the wishes of the body are right (observed), the wishes of the word as well, then are the wishes of the mind similar. Then all wishes are right (observed).
The thangka under review belonged once to a larger serie and was probably painted for the Ngor monastery. Another example from the same serie can be found in the Victoria and Albert Museum, London and is published by J. Lowry, Tibetan Art, London 1973, pp. 70-71.