Sura al-Furqān 25:53

وَهُوَ ٱلَّذِى مَرَجَ ٱلْبَحْرَيْنِ هَٰذَا عَذْبٌ فُرَاتٌ وَهَٰذَا مِلْحٌ أُجَاجٌ وَجَعَلَ بَيْنَهُمَا بَرْزَخًا وَحِجْرًا مَّحْجُورًا

wa-huwa alladhī maraja l-baḥrayni hādhā ʿadhbun furātun wa-hādhā milḥun ujājun wa-jaʿala baynahumā barzakhan wa-ḥijran maḥjūran

It is He Who has let free the two bodies of flowing water: One palatable and sweet, and the other salt and bitter; yet has He made a barrier between them, a partition that is forbidden to be passed.

Sura al-Faṭīr 35:12

وَمَا يَسْتَوِى ٱلْبَحْرَانِ هَٰذَا عَذْبٌ فُرَاتٌ سَآئِغٌ شَرَابُهُۥ وَهَٰذَا مِلْحٌ أُجَاجٌ وَمِن كُلٍّ تَأْكُلُونَ لَحْمًا طَرِيًّا وَتَسْتَخْرِجُونَ حِلْيَةً تَلْبَسُونَهَا وَتَرَى ٱلْفُلْكَ فِيهِ مَوَاخِرَ لِتَبْتَغُوا۟ مِن فَضْلِهِۦ وَلَعَلَّكُمْ تَشْكُرُونَ

wa-mā yastawī l-baḥrāni hādhā ʿadhbun furātun saʾighun sharābuhu wa-hādhā milḥun ujājun wa-min kullin taʾkulūna laḥman ṭariyyan wa-tastakhrijūna ḥilyatan talbasūnahā wa-tara l-fulka fīhi mawākhira li-tabtaghū min faḍlihi wa-la-ʿallakum tashkurūna

Nor are the two bodies of flowing water alike,- the one palatable, sweet, and pleasant to drink, and the other, salt and bitter. Yet from each (kind of water) do ye eat flesh fresh and tender, and ye extract ornaments to wear; and thou seest the ships therein that plough the waves, that ye may seek (thus) of the Bounty of Allah that ye may be grateful.