[25].Surah Al-Furqan [The Criterion]: Ayat 53

৫৩. তিনিই সমান্তরালে দুই সমুদ্র প্রবাহিত করেছেন, একটি মিষ্ট, তৃষ্ণা নিবারক ও একটি লোনা, বিস্বাদ; উভয়ের মাঝখানে রেখেছেন একটি অন্তরায়, একটি দুর্ভেদ্য আড়াল।
 

Ayat 53. And it is Allah Who has let free the two seas (kinds of water, Ocean and River), one palatable and sweet, and the other salt and bitter, and Allah set a barrier and a complete partition between them. 

[Tafseer] of Ayat 53. 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. Maraja: literally, let free or loose cattle for grazing. Bahrayn: two seas, or two bodies of flowing water: for bakris applied both to the salt sea and to rivers. In the world taken as a whole, there are two bodies of water, viz., (1) the great salt Ocean, and (2) the bodies of sweet water fed by rain, whether they are rivers, lakes, or underground springs: their source in rain makes them one, and their drainage, whether above ground or underground, eventually to the Ocean, also makes them one. They are free to mingle, and in a sense they do mingle, for there is a regular water cycle and the rivers flow constantly to the sea, and tidal rivers get sea water for several miles up their estuaries at high tide. Yet in spite of all this, the laws of gravitation are like a barrier or partition set by Allah, by which the two bodies of water as a whole are always kept apart and distinct. In the case of rivers carrying large quantities of water to the sea, like the Mississippi or the Yangtse-Kiang, the river water with its silt remains distinct from sea water for a long distance out to sea. But the wonderful Sign is that the two bodies of water, though they pass through each other, remain distinct bodies, with their distinct functions In Allah's overall scheme of things, bodies of salt and sweet water, which are adjoining and yet separate, have significant functions. Weaving a harmonious fabric out of these different fibers shows both Allah's power and wisdom. Incidentally, this verse points to a fact which has only recently been discovered by science. This fact relates to the oceans of the world: they meet and yet each remains separate for Allah has placed "a barrier, a partition" between them.

Hazrat Al-Mustuarad bin Shaddad (May Allah be pleased with him) reported: The Messenger of Allah [SAWW](PBUH) said, "This world (i.e., its pleasures and duration) in comparison with the Hereafter is (similar to the amount of water) one gets when he puts his finger in the sea. Let him then see what it returns with".

[Muslim Book 40, Chapter 14, Hadith # 6843]. 

Lesson : as mentioned above in Surah Al-Furqan Ayat 53."Allah Who has let free the two seas (kinds of water, Ocean and River)" This Hadith shows the value of the Hereafter and its blessings compared to the worldly life. The proportion between the two is that the former is like an ocean while the latter is like the proportion of water left on one's finger when dipped in the sea!.