Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
quran:25:53

And it is He who has released ˹simultaneously˺ the two seas, one fresh and sweet and one salty and bitter, and He placed between them a barrier and prohibiting partition.  

And He it is Who merged the two seas: letting them ˹flow˺ one adjacent to the other: this one palatable, sweet, and the other saltish, bitter; and He set between the two an isthmus, so that the one does not mix with the other, and a forbidding ban, a shield that prevents the two from becoming mixed.
القرآن:٢٥:٥٣

وَهُوَ الَّذِي مَرَجَ الْبَحْرَيْنِ هَٰذَا عَذْبٌ فُرَاتٌ وَهَٰذَا مِلْحٌ أُجَاجٌ وَجَعَلَ بَيْنَهُمَا بَرْزَخًا وَحِجْرًا مَحْجُورًا  

{وهو الذي مرج البحرين} أرسلهما متجاورين {هذا عذبٌ فرات} شديد العذوبة {وهذا مِلْحٌ أُجَاجٌ} شديد الملوحةِ {وجعل بينهما برزخا} حاجزا لا يختلط أحدهما بالآخر {وحجرا محجورا} سترا ممنوعا به اختلاطهما.