Dasatinib With Fludarabine and Rituximab in Relapsed and Refractory CLL and SLL

* Since the purpose of the study is to determine the response rate of the 3 drug regimen, everyone who participates will receive the same dose of the study drug, dasatinib and the 2 standard drugs, fludarabine and rituximab. * Participants will receive the drugs dasatinib, fludarabine, and rituximab at the following time points through each cycle of treatment. A cycle of study treatment is 28 days. Dasatinib pills will be taken orally each day for the first 2 weeks of each cycle. Fludarabine will be give intravenously on three days of each cycle (Days 3-5 in the first cycle, days 1-3 after that). Rituximab will be given intravenously with a total dose of 375 mg/m2 each cycle (split on Days 3+4 in the first cycle and at the discretion of the treating physician after that on Days 1-3). * The following procedures will be repeated throughout the study: medical history review; physical exam; performance status test; blood tests and EKG. They will occur daily during the first week of treatment, then weekly for the rest of cycle 1. After cycle 1 these procedures will be done once a week for 4 weeks then once a month for 6 months. * Tumor assessments will be repeated once every 2 months for the first six months of the study, and then once every 6 months after that. * Blood samples will be obtained in the first 5 days of treatment for pharmacokinetic studies and pharmacodynamic studies. * Participants that are benefiting from the study treatment after the first cycle can continue to receive an additional 6 cycles of study treatment.