Valmiki Ramayana Sundara Kanda Sarga 47 Shloka 31

वीरः brave, पवनात्मजः son of the Windgod, सः कपिः that Hanuman, वायुसेविते attended by the wind, पथि on the path, महाजवान् endowed with high speed, समाहितान् stable ones, विवर्तने in turning round, भारसहान् which could bear heavy loads, तान् those, अष्ट eight, हयान् horses, तलप्रहारैः by hitting with his palm, जघान killed

Hanuman the brave son of the Windgod hit with his palm and killed the eight horses (yoked to Aksha's chariot) which had great speed were stable and had the capacity to bear heavy loads while turning round in the sky. (The battle was fought in the air since Hanuman leaped into the air and the demon hero had to resist him there).