We study the Ξ b (6100) using the methods of QCD sum rules and light-cone sum rules within the framework of heavy quark effective theory. Our results suggest that the Ξ b (6100) can be well interpreted as the P -wave bottom baryon of J P = 3/2 − , belonging to the SU (3) flavor 3F representation. It has a partner state of J P = 1/2 − , labelled as Ξ b (1/2 − ), whose mass and width are predicted to be m Ξ b (1/2 − ) = 6.08 +0.13 −0.11 GeV and Γ Ξ b (1/2 − ) = 4 +29 − 4 MeV, with the mass splitting ∆M = m Ξ b (6100) − m Ξ b (1/2 − ) = 9 ± 3 MeV. We propose to search for it in the Ξc(1/2 − ) → Ξ b π decay channel. Our results also suggest that the Λ b (5912) and Λ b (5920) are their partner states with J P = 1/2 − and 3/2 − respectively, and moreover, the Λc(2595), Λc(2625), Ξc(2790), and Ξc(2815) are their charmed partner states.