39:21
أَلَمْ تَرَ أَنَّ ٱللَّهَ أَنزَلَ مِنَ ٱلسَّمَآءِ مَآءًۭ فَسَلَكَهُۥ يَنَٰبِيعَ فِى ٱلْأَرْضِ ثُمَّ يُخْرِجُ بِهِۦ زَرْعًۭا مُّخْتَلِفًا أَلْوَٰنُهُۥ ثُمَّ يَهِيجُ فَتَرَىٰهُ مُصْفَرًّۭا ثُمَّ يَجْعَلُهُۥ حُطَٰمًا ۚ إِنَّ فِى ذَٰلِكَ لَذِكْرَىٰ لِأُو۟لِى ٱلْأَلْبَٰبِ
Do you not see that Allah sends down rain from the sky and makes it flow as springs [and rivers] in the earth; then He produces thereby crops of varying colors; then they dry and you see them turned yellow; then He makes them [scattered] debris. Indeed in that is a reminder for those of understanding.
Translation · Saheeh International
Tafsir
Ibn Kathīr (abridged)
The Parable of the Life of this World
Allah tells us that water originates in the sky. This is like the Ayah:
وَأَنزَلْنَا مِنَ السَّمَآءِ مَآءً طَهُوراً
(and We send down pure water from the sky) (25:48). So, Allah sends down water from the sky, and it settles in the earth, then He causes it to flow wherever He wills, and He causes springs, great and small, to flow as needed. Allah says:
فَسَلَكَهُ يَنَابِيعَ فِى الاٌّرْضِ
(and causes it to penetrate the earth, as water springs,) Sa`id bin Jubayr and `Amir Ash-Sha`bi said that all the water on earth has its origins in the sky. Sa`id bin Jubayr said, its origins lie in the snow, meaning that snow piles up in the mountains, then settles at the bottom (of the mountains) and springs flow from the bottom of them.