Al-Kāfi - Volume 3 > The Timing of Salah (Prayer), the Beginning, the End and the Outstanding Phases
Hadith #4

4ـ مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ عَنْ فَضَالَةَ بْنِ أَيُّوبَ عَنْ مُعَاوِيَةَ بْنِ عَمَّارٍ أَوِ ابْنِ وَهْبٍ قَالَ قَالَ أَبُو عَبْدِ الله (عَلَيْهِ الْسَّلام) لِكُلِّ صَلاَةٍ وَقْتَانِ أَوَّلُ الْوَقْتِ أَفْضَلُهُمَا.

4. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from al-Husayn ibn Sa‘id from Fadalah ibn Ayyub Mu‘awiyah ibn ‘Ammar or ibn Wahab who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said, ‘For every Salah (prayer) there are two kinds of timings and the outstanding one is the beginning of time.’”