It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that a man said near the Jamrah: O Messenger of Allah, which jihad is best? He (peace and blessings be upon him) said: "The best jihad is a word of truth before an oppressive ruler."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 8050