The 34th of the 42 hadiths gathered by Imam Yahya ibn Sharaf an-Nawawi in An-Nawawi's Forty Hadith, given below in the original Arabic with an English translation and its reference.
عَنْ أَبِي سَعِيدٍ الْخُدْرِيّ رَضِيَ اللهُ عَنْهُ قَالَ سَمِعْت رَسُولَ اللَّهِ صلى الله عليه و سلم يَقُولُ: مَنْ رَأَى مِنْكُمْ مُنْكَرًا فَلْيُغَيِّرْهُ بِيَدِهِ، فَإِنْ لَمْ يَسْتَطِعْ فَبِلِسَانِهِ، فَإِنْ لَمْ يَسْتَطِعْ فَبِقَلْبِهِ، وَذَلِكَ أَضْعَفُ الْإِيمَانِ . [رَوَاهُ مُسْلِمٌ]
On the authority of Abu Sa`eed al-Khudree (may Allah be pleased with him) who said: I heard the Messenger of Allah (ﷺ) say, “Whosoever of you sees an evil, let him change it with his hand; and if he is not able to do so, then [let him change it] with his tongue; and if he is not able to do so, then with his heart — and that is the weakest of faith.” [Muslim]
Text from the open hadith-api dataset. Hadith numbering follows that edition and can differ slightly from a printed copy — check the Arabic against a trusted mushaf of hadith before relying on a reference.