Rabi’ al-Awwal 29, 1330
The order was one that required its execution as such; so, nobody would understand it any other way; therefore, calling it a recommendation is not proved by any argument at all. On the contrary, proofs emphasize its real meaning, i.e. as an order; so, look carefully into those traditions and you will find out that what we say here is the truth.
Suffices you his statement (pbuh): "This man and his men read the Qur'an only pronouncing its words [just to impress people]; they depart from the faith as swiftly as the arrow departs from the bow, and they do not go back till the arrow goes back to the bow anew. Kill them, for they are the worst among the living," and also his statement, peace be upon him and his progeny, "Had he been killed, no two men of my nation will have ever disputed with one another." Such statements were not said except when there was a serious command greatly emphasizing that the man be killed.
If you refer to Ahmad's Musnad, you will find the order to kill the man was directed to Abu Bakr in particular, then to ‘Umar in particular; so, how can the obligation be ruled out?
Yet traditions are indeed explicit in indicating that those companions refrained from killing the man only because they hated to do so for no reason other than the fact that he was engaged in prayer and supplication. They did not feel well even though the Prophet (pbuh) himself felt well about getting rid of him.
They did not abide by the order which they had received from the Prophet (pbuh) to kill the man. This incident, therefore, is just another proof testifying to the fact that they used to prefer to follow their own opinions rather than the instructions of the Prophet (pbuh), Wassalam.