In shiv puran it is mentioned in Rudrasamihta that shiva rubbed his 10% of left side body with Amrit and Vishnu appeared and the name vishnu was given by shiva .It is also mentioned that Brahma was also created by Shiva and then placed him in the lotus that originated from the navel of lord vishnu.
For shiva It is written in the same book that he is the physical form of Nirakaar.