Hadithcore
Riyad as-Salihin, 195

Abu 'Abdullah Tariq bin Shihab (May Allah bepleased with him) reported:

A person asked the Prophet (ﷺ) (when he had just put his foot in the stirrup): "What is the highest form of Jihad?" He (ﷺ) said, "Speaking the truth in the presence of a tyrant ruler". <b>[An-Nasa'i, with a sound chain]</b>.

الثاني عشر‏:‏ عن أبي عبد الله طارق بن شهاب البجلي الأحمسي رضي الله عنه أن رجلاً سأل النبي صلى الله عليه وسلم، وقد وضع رجله في الغرز‏:‏ أي الجهاد أفضل‏؟‏ قال‏:‏ “كلمة حق عند سلطان جائر‏"‏ ‏(‏‏(‏رواه النسائي بإسناد صحيح‏)‏‏)‏‏.‏

References1 variant
In-Book Reference
Introduction, Hadith 195
Sharh · explanationclick to expand
<b>Guidance from the Hadiths:</b><br> 1) Saying a word of truth to an unjust ruler is one of the greatest forms of Jihad, as it deters him from his injustice.<br> 2) Giving sincere advice to unjust rulers is obligatory, along with enjoining them to do good and forbidding them from doing evil.<br> <br> <b>Benefit:</b><br> Expressing disapproval of the ruler’s actions falls under four categories:<br> 1) A word of truth said to a just ruler, which is an easy mission.<br> 2) A word of falsehood said to a just ruler. This word is perilous as it is a source of trial to the ruler and the sayer.<br> 3) A word of truth said to an unjust ruler. This is the best form of Jihad.<br> 4) A word of falsehood said to an unjust ruler. This is misguidance to the Ummah.