‘Abdullāh ibn Mughaffal (may Allah be pleased with him) reported that the Messenger (may Allah's peace and blessings be upon him) said: "Offer two Rak‘ahs before Maghrib." Then he said: "Offer two Rak‘ahs before Maghrib, if you will," fearing people might take it as Sunnah.
In this Hadīth, the Prophet (may Allah's peace and blessings be upon him) encourages us to offer two Rak‘ahs before the Maghrib prayer, after the Adhān, on a supererogatory basis for those who will. These two Rak‘ahs, however, are not among the confirmed regular Sunnah prayers. So, it is recommended not to offer them persistently, lest they will be like the other regular ones. The two Rak‘ahs before Maghrib are established through three forms: The Prophet instructed us to offer them, as in this Hadīth; he offered them, as in the narration by Ibn Hibbān; and he saw the Companions offer them and approved their act.