"Allah's Messenger prayed Maghrib when the sun had set and it (the sun) had hidden in the veil (of darkness)."
Jami` at-Tirmidhi Book 2, Hadith 16
← Previous Hadith Isma'il ibn Ulayyah narrated to him from Ibn Juraij. This latter chain is more correct.

Jami` at-Tirmidhi Book 2, Hadith 15 Next Hadith → "I am the most knowledgeable among the people about the prescribed time of this prayer: Allah's Messenger would pray it when the moon set on the third (of the month)."

Jami` at-Tirmidhi Book 2, Hadith 17