Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Abdullah Muzani that the Messenger of Allah (peace and blessings of Allah be upon him) offered two rak‘ahs before Maghrib and said: "Offer two rak‘ahs before Maghrib, (offer two rak‘ahs before Maghrib)." Then, the third time he said: "Whoever wishes may offer them." The Prophet (peace and blessings of Allah be upon him) feared that people might consider it a (mandatory) Sunnah or a fixed practice.