First: he must know what is right and what is wrong. Without this knowledge, he cannot properly enjoin or forbid anything, since he may unwittingly forbid what is right or enjoin what is wrong.
Second: he must be confident that his forbidding a wrong will not lead to a greater wrong—for example, forbidding someone to drink wine only for this to lead to someone being killed, or something similar. If he cannot be confident of this, he may neither enjoin nor forbid.
Third: he must know, or consider it most likely, that his forbidding the wrong will put an end to it, and that his enjoining what is right will be effective and beneficial. If he neither knows this nor considers it most likely, he is not obliged to enjoin or forbid.
The first and second conditions thus determine permissibility, while the third determines obligation. If the first and second conditions are not met, he may neither enjoin nor forbid. If the third condition is absent but the first two are met, he may enjoin and forbid, but is not obliged to do so. Nevertheless, it is recommended for him, even if he considers it most likely that the person will not heed him, for perhaps he will eventually do so—especially if he treats him gently. Allah, Mighty and Majestic, says:
“Speak to him gently, so that perhaps he may take heed or stand in awe.” [Tā Hā: 44]
It is reported that a man from among the Prophet’s Companions, blessings and peace be upon him, was in Syria and became heavily addicted to wine. When news of this reached ‘Umar ibn al-Khattāb, he wrote to him:
“Hā Mīm. The revelation of this Book is from Allah, the Almighty, the All-Knowing.” [Ghāfir: 1–2]
“The Forgiver of sin and Accepter of repentance, severe in punishment, and limitless in bounty. There is no god but Him. To Him is the final return.” [Ghāfir: 3]
The man then gave up wine, repented of drinking it, and abandoned it.
If a man sees either of his parents committing a wrong, he should admonish them gently and address them respectfully about it, as Allah has commanded him:
“If one or both of them reach old age in your care, never say to them even ‘ugh,’ nor rebuke them.” [al-Isrā’: 23]
Through to His words:
“And say, ‘My Lord, have mercy on them, as they raised me when I was small.’” [al-Isrā’: 24]
The evidence that this is obligatory under the conditions mentioned is the statement of Allah, Mighty and Majestic: