Silsilat al-Ahadith al-Sahihah

The Messenger of Allah (peace and blessings be upon him) said: "The most virtuous form of jihad is to speak a word of justice (or a word of truth) before a tyrant ruler." This hadith is narrated from Sayyiduna Abu Sa'id Khudri, Sayyiduna Abu Umamah, Sayyiduna Tariq bin Shihab, and Sayyiduna Jabir bin Abdullah (may Allah be pleased with them), and it is also reported mursal from Imam Zuhri.