Ibrahim signed in January 2013 from Celtic, with Reuben following three months later from Kano Pillars in his homeland.
Reuben requested that he be released from the remainder of his contract to enable him to seek a new challenge elsewhere, while former Celtic player Ibrahim left the club by mutual agreement in search of regular first-team football.
Reuben, capped 10 times by his country, moved to Rugby Park in April 2013 but made only three appearances in an injury-hit eight months.
After signing, he was ruled out for three months through injury, and only made his debut days after criticising his treatment by the club and handing in a transfer request.
The 23-year-old has not featured since being sent off in a 4-1 defeat by Dundee United in December.
He had moved to the Ayrshire club at the same time as compatriot Papa Idris but his former Kano Pillars and international team-mate was released in June after failing to feature under previous Kilmarnock manager Kenny Shiels.
Ibrahim, 22, made 17 appearances after moving from Parkhead in January 2013 but has not played for the club since being stretchered off after 35 minutes of the 2-0 Scottish Premiership home victory over Ross County in October.
A club statement said: "Everyone at Kilmarnock Football Club thanks Gabriel and Rabiu for their respective contributions and wishes them every success in the future.
"Both players have expressed their thanks to the Club's staff and supporters for the warm welcome which they received and wish the club the best of luck in 2014 and beyond."