Musannaf Ibn Abi Shaybah 9810 — Those who disliked perpetual fasting

Amr bin Shurahbil says that a man said: "O Messenger of Allah! Can a man fast perpetually?" He said: "In my view, he should not fast the whole of time." The questioner said: "Can he fast two-thirds of it?" He said: "That too is too much." He said: "Can he fast half of it?" He said: "That too is too much." Then he said: "I shall tell you of an amount by which the whisperings and the rancour of his heart will be removed: let him fast three days every month."