(37) باب فَضْلِ مَنْ تَكَلَّمَ بِالْحَقِّ عِنْدَ إِمَامٍ جَائِرٍ
It was narrated from Tariq bin Shihab that:
a man asked the Prophet, when he had put his leg in the stirrup: "Which kind of Jihad is best?'" He said: " a word of truth spoken before an unjust rulers."
Reference: Sunan an-Nasa'i 4209
In-book reference: Book 39, Hadith 61
English translation: Vol. 5, Book 39, Hadith 4214