Hadith 1124

Anas (May Allah be pleased with him) reported: In the lifetime of the Messenger of Allah (PBUH), we used to perform two Rak'ah (optional prayer) after sunset before the Maghrib prayer. It was asked: "Did Messenger of Allah (PBUH) perform them?" He replied: "He saw us performing it, but he neither ordered us to perform them nor did he forbid us from doing so."

[Muslim].