Yahya related to me from Malik from Ibn Shihab from Humayd ibnAbd ar-Rahman that Umar ibn al-Khattab and Uthman ibn Affan would praymaghrib when they saw the night darkening, before they broke theirfast, and that was during Ramadan.
USC-MSA web (English) reference: Book 18, Hadith 8
Arabic reference: Book 18, Hadith 641