"إذا أممت الناس: فاقرأ ب {وَالشَّمْسِ وَضُحَاهَا} و {سَبِّحِ اسْمَ رَبِّكَ الْأَعْلَى} و {وَاللَّيْلِ إِذَا يَغْشَى}
The Prophet (peace and blessings be upon him) said:
"When you lead the people in prayer, recite (in the prayer) 'By the sun and its brightness' [Surah al-Shams: 1], 'Glorify the name of your Lord, the Most High' [Surah al-A'la: 1] and 'By the night when it covers' [Surah al-Layl: 1]."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 393