Assalamu alikum in 18:86 of the quran what is this ayn some say spring but some say a spring is to small to look like it's setting please answer this I know you have answered a similar question but that doesn't explain ayn and that it is to small to look a sun is setting in it jazzakkALLAH

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The meaning of the Arabic word ‘Ayn (translated as ‘spring’) in the verse is the ocean, as stated by the scholars of Tafseer, because the word ‘Ayn is used in Arabic to refer to a spring of water, and this description applies to the small and the large springs alike. Ibn Katheer said in his book Tafseer Ibn Katheer (revised by Salaamah) (5/191): “His Saying (what means): {…he found it [as if] setting in a spring of dark mud,} [Quran 18:86] means that he saw the sun setting into the ocean from his standpoint. This is something which everyone who reaches the coast can see; it looks as if the sun is setting into the ocean.” [End of quote]

The author of Adhwaa’ Al-Bayaan fi Eedhaah Al-Quraan bil-Quraan (3/341) said as he commented on the above words of Ibn Katheer: “His statement means that the word ‘Ayn used in the verse refers to the ocean, which has murky mud. The word ‘Ayn is used in Arabic to refer to a spring, which is a large amount of water. So, linguistically speaking, the word ‘Ayn may also refer to the sea. The fact that a beholder standing by the coastline of the Western Ocean sees the sun as if it is setting into the ocean from his standpoint is known. Based on this interpretation, there is no problematic aspect in the (meaning of the) verse and Allah Knows best.” [End of quote]

As-Sa‘di also said in his Tafseer: “Allah, The Exalted, Says (what means): {…he found it [as if] setting in a spring of dark mud,} [Quran 18:86] means that he saw the sun as if setting into the sea (according to the perception of his eyes), and the sea's color was black as mud.” [Tayseer Al-Lateef Al-Mannaan fi Khulaasat Tafseer Al-Quran, (1260)]

To sum up the relevant statements of the Quran commentators: “When he reached the coastline, he stood to look at the sunset, and saw the sun – from his vantage point - as if it was setting into a spring of hot blazing fire, because of the very reddish solar disc that appears as a blaze. This made the spot into which it disappeared seem to him like a hot spring. As a beholder would see the sun as if it is setting into a hot spring according to the perception of his eyes, he imagines that it sets into a murky and muddy spring. When the sun sets and disappears into the water, the spot where it disappears becomes dark and faded after it was glowing.” [End of quote, At-Tafseer Al-Waseet - Al-Azhar Islamic Research Academy (AIRA) (6/918)]

For more benefit regarding the sun setting into water spring, please refer to Fataawa 340585, 315658, and 253912.

Allah Knows best.