In the eighteenth incarnation, the Lord appeared as King Rāma. In order to perform some pleasing work for the demigods, He exhibited superhuman powers by controlling the Indian Ocean and then killing the atheist King Rāvaṇa, who was on the other side of the sea.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
नरदेवत्वमापन्नः सुरकार्यचिकीर्षया । समुद्रनिग्रहादीनि चक्रे वीर्याण्यतः परम्
naradevatvamāpannaḥ surakāryacikīrṣayā | samudranigrahādīni cakre vīryāṇyataḥ param
SB 1.3.22