Different practices regarding the Witr prayer have been reported from the Prophet (peace be upon him). Based on these narrations, the imams of the legal schools exercised ijtihad, which led to differing juristic opinions and corresponding rulings within each school. Performing the prayer in the form of 2+1 is among these reported practices.
According to the Hanafi school, when performing the Witr prayer individually, it is prayed as three rak‘ahs with two sittings (tashahhud). However, there is no objection to following an imam from another school who performs the Witr prayer in the form of 2+1.