Sayyiduna Abu Ubaydah bin al-Jarrah (may Allah be pleased with him) narrates: I said: "O Messenger of Allah! Which of the martyrs is most honoured in the sight of Allah Almighty?" The Prophet (peace and blessings be upon him) said: "A man who stands before an unjust ruler and enjoins him to good or forbids him from evil, and that ruler has him killed." It was asked: "Who among people will receive the severest punishment?" The Prophet (peace and blessings be upon him) said: "A man who has killed a prophet, or has killed a man who enjoined him to some good or forbade him from evil." Then he recited this verse: "And they kill the prophets without right and kill those among people who enjoin justice; so give them tidings of a painful punishment." Then the Prophet (peace and blessings be upon him) said: "O Abu Ubaydah! The Children of Israel killed forty-three prophets (peace be upon them) at one time, and one hundred and twelve men of the worshippers among the Children of Israel rose up, enjoined good and forbade evil, and they were all killed."
Al-Bazzar recorded it, and its chain contains two narrators whom I do not know.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الفتن - أعاذنا الله منها / 12166