It is correct that knowledge is a common property. But it does not mean that people cannot own their materials like books. It does not mean that people can go and steal books or take over other people’s labs and libraries. It means that all people should be free to learn. No single group should have monopoly on knowledge. Thus the meaning of this Hadith is to seek knowledge from all sources, not to take over other people’s possession. Islam encourages Muslims to learn, but it also respects the laws of ownership. Plagiarism, piracy, misquotation, taking other people’s property etc. are all nothing but theft, and deception. People have right to their material property.