حَدَّثَنَا عَمْرُو بْنُ عَلِيٍّ، عَنْ صَفْوَانَ بْنِ عِيسَى، عَنْ يَزِيدَ بْنِ أَبِي عُبَيْدٍ، عَنْ سَلَمَةَ بْنِ الأَكْوَعِ، قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم يُصَلِّي الْمَغْرِبَ سَاعَةَ تَغْرُبُ الشَّمْسُ إِذَا غَابَ حَاجِبُهَا ‏.‏

Salamah b. al-Akwa' said: The Prophet (PBUH) used to say the Maghrib prayer immediately after the sun had set when its upper side would disappear. Translation Not Available

Book Ref: Sunan Abi Dawud Book 2 Hadith 417
Web Ref:  Sunan Abi Dawud Book 2 Hadith 417