From Halopedia, the Halo wiki
Killed a Spartan-II during the Harvest campaign
Ustaf 'Nbekee is a Sangheili. He killed an unidentified Spartan-II during the Harvest campaign in early 2531 at a Methane refinery near the relic the Covenant found. 'Nbekee then sent a message to his Clan brother 'Crolunee in which he bragged about his victory.