A man asked the Prophet ﷺ, while he had already placed his foot in the stirrup, "Which jihad is best?"He replied, "A word of truth before a tyrannical ruler."
أن رجلا سأل النبي ﷺ وقد وضع رجله في الغرز: أي الجهاد أفضل؟ قال: كلمة حق عند سلطان جائر.
Nasai (4209) and Ahmad (18828, 18830) narrated it through several routes from Sufyan (that is, Thawri), from Alqama bin Marthad, from Tariq bin Shihab, who related it. Its chain of transmission is sahih, and Tariq bin Shihab saw the Prophet ﷺ but did not hear from him, so his narration falls under the category of a companion's mursal report, which is considered authoritative.