Is not hearing something yet affirming that one heard it considered a false testimony (Shahadat Az-Zour)? And what is its expiation?

It is not permissible for a Muslim to bear witness to something the occurrence of which he does not know to be true, based on the Almighty's saying: "And we did not testify except to what we knew." And upon whoever did that is sincere repentance and not returning to such an act. If his testimony resulted in the destruction of property, then he must guarantee what was destroyed because of it, unless the owner of the right waives his right.