All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
It has been reported that the Prophet called the athaan and the iqaamah (second and final call to prayer) in some occasions. An-Nawawi wrote:
"Based on the evidence highlighted by the compiler, it is an act of the Sunnah to call the athaan in a standing position in the direction of the Qiblah (prayer direction: Ka'bah in Makkah). It is disliked, yet valid, to call the athaan while sitting or laying down or not facing the Qiblah because the intended purpose of calling the athaan is to inform the people of the time of prayer, and this objective is fulfilled in this case. This has been stated by the majority of the scholars. Iraqi scholars and most of the scholars of Khorasan held this view with no conditions; it is the reported opinion in this regard. Groups of scholars from Khorasan, on the other hand, maintained that there are two views regarding calling the athaan in a standing position and in the direction of the Qiblah as long as the person is able to do so. Al-Qaadhi Husayn cited one view in this regard that says that it is valid to call the athaan in a sitting position but not a lying position. The view of our school of Fiqh is that calling the athaan is valid in all of these positions. This is evidenced by the hadeeth narrated on the authority of Yaʻla ibn Murrah that says that they were with the Prophet on a journey. They wound up in a narrow area when the prayer became due. Then, it began raining from the sky above them, and it was wet beneath them. So the Prophet called the athaan while he was on his mount, and then the iqaamah, going forward (to be ahead of them) on his mount. He led them in the prayer by moving his head up and down, making his prostrations lower than his bowing. The hadeeth was narrated by At-Tirmithi with a good chain of narration. This prayer was an obligatory one, and this is why the Prophet called the athaan and the iqaamah and led the prayer while he was on his mount, given the valid excuse ..." [Al-Majmooʻ]
Allaah knows best.