It is narrated from Hafs bin Asim that the Prophet (peace and blessings be upon him) heard a man giving the adhan for Maghrib, and the Prophet (peace and blessings be upon him) said the like of what he said. Then he (peace and blessings be upon him) reached him as he said: The prayer has been established. The Prophet (peace and blessings be upon him) said: "Dismount." Then they prayed Maghrib with the iqamah of that black slave.
This is mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1919