Vishnu, Agni (the god of fire) and Soma formed the shaft of that bow. The entire was universe of nothing but Agni and Soma. The universe is also to consist of Vishnu.
इषुश्चाप्यभवद् विष्णुर्व्वलनः सोम एव च। अग्नीषोमौ जगत् कृत्स्नं वैष्णवं चोच्यते जगत्॥