Search for the Decay Bto D_(s1)⁺(2536)X

Using data recorded by the CLEO II detector at CESR, we have searched for the decay B -> Ds1+(2536) X, where Ds1+ is the narrow P-wave D_s^+ meson with J^P=1^+. The upper limit to the inclusive branching fraction is measured to be Br(B -> Ds1+ X) < 0.95% at the 90% confidence level. This limit is small compared with the total expected B -> Dbar(*)D(*)KX rate. Assuming factorization, the Ds1+ decay constant is constrained to be f_Ds1 < 114 MeV at the 90% confidence level, which is at least 2.5 times smaller than that of Ds+.