Maliks Muwatta Book 43, Hadith Number 13.

Section : Killing Secretly by Trickery and Sorcery.

Yahya related to me from Malik from Yahya ibn Said from Said ibn al-Musayyab that Umar ibn al-Khattab killed five or seven people for one man whom they had killed secretly by trickery. Umar said, “Had all the people of Sana joined forces against him, I would have killed them all.”