Abu Omar al-Saif (Arabic: أبو عمر السيف‎)(1968/69-2005) was an informal name or nom de guerre of a Saudi Islamist and fighter operating first in Afghanistan (1986–1988) and later in the North Caucasus (1996–2005) as the mufti of Arab fighters in Chechnya, allegedly with close ties to al-Qaeda. His full name was Muhammad bin Abdullah bin Saif al-Buainain (محمد بن عبد الله بن سيف البوعينين). He sometimes also used the name, or was addressed as, al-Jaber. He was born in 1968 or 1969 in Saudi Arabia, and was killed in Dagestan in December 2005.