۞ وَهُوَ الَّذِيْ مَرَجَ الْبَحْرَيْنِ هٰذَا عَذْبٌ فُرَاتٌ وَّهٰذَا مِلْحٌ اُجَاجٌۚ وَجَعَلَ بَيْنَهُمَا بَرْزَخًا وَّحِجْرًا مَّحْجُوْرًا ( الفرقان: ٥٣ )
Wa Huwal lazee marajal bahraini haazaa 'azbun furaatunw wa haazaa milhun ujaaj; wa ja'ala bainahumaa barzakhanw wa hijram mahjooraa (al-Furq̈ān 25:53)
And it is He who has released [simultaneously] the two seas [i.e., bodies of water], one fresh and sweet and one salty and bitter, and He placed between them a barrier and prohibiting partition. (Al-Furqan  : 53)
1 Mufti Taqi Usmani
He is the One who joined the two seas, so as this is sweet, very sweet, and this is bitter, very bitter, and made between them a buffer and an insurmountable barrier.