Abu Abdillah Mohammad bin Wahban Al-SALI narrated from Ahmad bin Aman Al-Amery, from Abdullah bin Abdillah bin Otaba bin Abdillah bin Masoud, from his father, from his grandfather, Abdullah bin Masoud, who said:
I heard the MESSENGER OF ALLAH (SAWW) say, “The sun has two sides: one side gives light to the inhabitants of the heavens, and one side gives light to the inhabitants of earth. There is writing on both sides. Do you know what is written (on both sides of the sun)?”
We replied, “ALLAH (SWT) and His MESSENGER (SAWW) know better.”
The PROPHET (SAWW) said, “The writing on the side that gives light to the heavens says, ‘ALLAH (SWT) is the light of the heavens and earth' (24:35).
The writing on the side that gives light to the inhabitants of earth says, ‘ALI (ASWS) is the light of the earths.’
(Ref: Bihar Volume 27 Page 9 Hadees No.21)