The weak decays Ξ b→Λ b π and Ξ c→Λ c π , in which the heavy quark is not destroyed, are discussed. The branching fractions for these decays, corresponding to an absolute rate of order 0.01 ps −1 , should be at a one percent level for the b hyperons and at a (few) per mill level for Ξ c , possibly making feasible their experimental study in future. It is shown, through an application of the heavy quark limit, the flavor SU(3) symmetry, and PCAC, that the ΔI=1/2 rule should hold very well in these decays, and also that the Ξ b decays are purely S wave in the symmetry limit, while the difference between the S wave amplitudes of the Ξ c decays and those for the Ξ b is related, in terms of the heavy quark expansion, to the difference of the total decay rates within the ( Ξ c, Λ c ) triplet of charmed hyperons. We also comment on the amplitudes of the semileptonic transitions Ξ Q→Λ Q ℓ ν and on the weak radiative decays Ξ Q→Λ Q γ .