Q text from Luke and Matthew is the other early source. From Wikipedia Q source:
Along with Markan priority, Q was hypothesized by 1900, and it is one of the foundations of most modern gospel scholarship. B. H. Streeter formulated a widely accepted view of Q: that it was a written document (not an oral tradition) composed in Greek; that almost all of its contents appear in Matthew, in Luke, or in both; and that Luke more often preserves the original order of the text than Matthew. In the two-source hypothesis, Matthew and Luke both used Mark and Q as sources.