Hadithcore
Hadith #506410

Yahya related to me from Malik from Ibn Shihab from Humayd ibn Abd ar-Rahman that Umar ibn al-Khattab and Uthman ibn Affan would pray maghrib when they saw the night darkening, before they broke their fast, and that was during Ramadan.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، وَعُثْمَانَ بْنَ عَفَّانَ، كَانَا يُصَلِّيَانِ الْمَغْرِبَ حِينَ يَنْظُرَانِ إِلَى اللَّيْلِ الأَسْوَدِ قَبْلَ أَنْ يُفْطِرَا ثُمَّ يُفْطِرَانِ بَعْدَ الصَّلاَةِ وَذَلِكَ فِي رَمَضَانَ ‏.‏

References1 variant
Arabic/English book reference
Book 18, Hadith 8