  We study nonleptonic Lambda_b -> Lambda_c pi, Sigma_c pi and Sigma_c^* pi
decays in the limit m_b, m_c, E_pi >> Lambda_{QCD} using the soft-collinear
effective theory. Here Sigma_c = Sigma_c(2455) and Sigma_c^* = Sigma_c(2520).
At leading order the Lambda_b -> Sigma_c^{(*)} pi rates vanish, while the
Lambda_b -> Lambda_c pi rate is related to Lambda_b -> Lambda_c\ell\bar\nu, and
is expected to be larger than Gamma(B -> D^{(*)} pi). The dominant
contributions to the Lambda_b -> Sigma_c^{(*)} pi rates are suppressed by
Lambda_{QCD}^2/E_pi^2. We predict Gamma(Lambda_b -> Sigma_c^* pi) /
Gamma(Lambda_b -> Sigma_c pi) = 2 + O[Lambda_{QCD}/m_Q, alpha_s(m_Q)], and the
same ratio for Lambda_b -> Sigma_c^{(*)} rho and for Lambda_b -> Xi_c^{(',*)}K.
``Bow tie'' diagrams are shown to be suppressed. We comment on possible
discovery channels for weakly decaying pentaquarks, Theta_{b,c} and their
nearby heavy quark spin symmetry partners, Theta_{b,c}^*.
