Shiva Purana
एवं द्वीपास्समुद्रैस्तु सप्त सप्तभिरावृताः ॥ द्वीपाश्चैव समुद्राश्च समाना द्विगुणैः परैः ॥ ६८ ॥
Thus the seven continents are surrounded by seven oceans each twice as large as the one within.
english translation
evaM dvIpAssamudraistu sapta saptabhirAvRtAH ॥ dvIpAzcaiva samudrAzca samAnA dviguNaiH paraiH ॥ 68 ॥
hk transliteration by Sanscript