It is narrated from al-Hasan (may Allah have mercy on him) that the Messenger of Allah (peace and blessings be upon him) gave Sayyiduna Bilal (may Allah be pleased with him) an order during a journey, and he gave the adhan on his mount. Then they dismounted and prayed two rak'ahs; then he was ordered and gave the iqamah, and he (peace and blessings be upon him) led them in the morning prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1843