Tafsir of At-Tawbah 9:73

{O Prophet, strive against the disbelievers} with the sword, {and the hypocrites} with argument.

{And be harsh with them} in both forms of striving. Do not show them favoritism. Regarding anyone who is found to hold corrupt beliefs, this ruling applies to them: they are to be striven against with argument, and harshness is to be employed toward them as much as possible.

Ibn Mas‘ud said: "If one cannot [strive] with his hand, then with his tongue; if he cannot, then let him scowl in their face; and if he cannot, then with his heart." He means [by this] hatred, loathing, and disavowal of them.

Al-Hasan interpreted the striving against the hypocrites as the implementation of legal penalties (hudud) upon them if they commit the acts that warrant them.

{They swear by Allah that they did not say [it], but they did say the word of disbelief and disbelieved after their Islam, and they planned that which they did not attain. And they did not resent except that Allah and His Messenger had enriched them from His bounty. So if they repent, it is better for them; but if they turn away, Allah will punish them with a painful punishment in this world and the Hereafter, and there will not be for them on earth any protector or helper.}