A novel distributed fountain coding scheme for three-source single-relay networks is proposed. First, the robust Soliton distribution (RSD) is threefoldly deconvolved to get the degree distribution for each source performing encoding. Then the single relay performs re-encoding using certain degree distribution. The asymptotic performance of distributed fountain codes with three sources (DFC-3) is analyzed by the And-Or tree technique. Simulations of the proposed DFC-3 are evaluated and compared with other fountain coding schemes. Simulation results show that the overall degree distribution of DFC-3 is consistent with RSD, and the BER performance agrees with the results of asymptotic analysis. It also reveals that DFC-3 have good performance on lossless channels.