Tawus (may Allah have mercy on him) said: Ibn Umar (may Allah be pleased with them both) was asked about the two rak'ahs before Maghrib, and he said: I did not see anyone in the time of the Prophet (peace and blessings be upon him) praying two rak'ahs before Maghrib; and he permitted praying two rak'ahs after Asr.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4505