Both Tesla and Toyota have sung each other's praises in the not-too-distant past, Toyota telling Autoblog back in May, "We have a good relationship with Tesla and will evaluate the feasibility of working together on future projects." According to Automotive News, Musk said of the Japanese giant, "We love working with Toyota... We have a huge amount of respect for them as a company and certainly much to learn."
Interestingly, though, the two automakers have rather divergent strategies for eco-friendly automobiles. Toyota, as you're surely aware, is the clear-cut leader in hybrids and has thrown its massive support in the direction of hydrogen fuel cells, while Tesla has invested heavily in battery-electric technology and high-speed charging stations.
Still, both hybrids and fuel cell vehicles still require battery packs, albeit ones smaller than pure EVs, so it's not an off-the-wall suggestion that Toyota could work with Tesla in the coming years on such diverse products. For the time being, Toyota has responded that it has "nothing to say" about Musk's suggestions of future collaboration.