Sayyiduna Abdullah bin Mughaffal (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "Between the adhan and the iqamah there is a prayer." Then the third time he (peace and blessings be upon him) said: "It is for whoever wishes." The narrator said that Ibn Buraydah (may Allah have mercy on him) used to pray two rak'ahs before Maghrib.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4493