We design and fabricate a tough elastomer by hybridizing a covalently crosslinked network with reversible hydrogen bonds, circumventing the immiscibility between networks formed by non-polar permanent and polar reversible bonds without solvents. Similar to sacrificial bonds in biological tissues, the reversible bonds break and reform, surprisingly forming crazes that typically exist in plastics and glass; this enables efficient energy dissipation and maintains material integrity upon large deformation, resulting in an elastomer with fracture toughness higher than that of natural rubber and a recent record of tough elastomers formed by interpenetrating covalently crosslinked networks. Our discovery suggests a new route towards tough elastomers, provides a model system to explore the mechanism of deformation and energy dissipation, and broadens the applications of elastomers.