When you see something wrong happening
Three levels, in descending order of capacity.
مَنْ رَأَى مِنْكُمْ مُنْكَرًا فَلْيُغَيِّرْهُ بِيَدِهِ فَإِنْ لَمْ يَسْتَطِعْ فَبِلِسَانِهِ فَإِنْ لَمْ يَسْتَطِعْ فَبِقَلْبِهِ وَذَلِكَ أَضْعَفُ الإِيمَانِ
Whoever among you sees a wrong, let him change it with his hand. If he cannot, then with his tongue. If he cannot, then with his heart, and that is the weakest of faith.
The last option is still counted as faith. Being unable to act is not the same as not caring.
The full narration
It is narrated on the authority of Tariq b. Shihab:It was Marwan who initiated (the practice) of delivering khutbah (address) before the prayer on the 'Id day. A man stood up and said: Prayer should precede khutbah. He (Marwan) remarked, This (practice) has been done away with. Upon this Abu Sa'id remarked: This man has performed (his duty) laid on him. I heard the Messenger of Allah as saying: He who amongst you sees something abominable should modify it with the help of his hand; and if he has not strength enough to do it, then he should do it with his tongue, and if he has not strength enough to do it, (even) then he should (abhor it) from his heart, and that is the least of faith
Source
Ṣaḥīḥ Muslim · 177
- Agreed upon as authentic (al-Bukhārī / Muslim)