Hadithcore
Mishkat al-Masabih, 3705, 3706

He reported God’s Messenger as saying, “The most excellent <i>jihad</i> is when one speaks a true word in the presence of a tyrannical ruler.” Tirmidhi, Abu Dawud and Ibn Majah transmitted it, and Ahmad and Nasa‘i transmitted it on the authority of Tariq b. Shihab.

وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «أَفْضَلُ الْجِهَادِ مَنْ قَالَ كَلِمَةَ حَقٍّ عِنْدَ سُلْطَانٍ جَائِرٍ» . رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُد وَابْن مَاجَه وَرَوَاهُ أَحْمَدُ وَالنَّسَائِيُّ عَنْ طَارِقِ بْنِ شِهَابٍ

References1 variant
In-Book Reference
Book 18, Hadith 45