[Machine] Ibn Umar might have called for prayer on his journey at dawn, then he would set up on the ground.  

كَانَ ابْنُ عُمَرَ رُبَّمَا أَذَّنَ عَلَى رَاحِلَتِهِ الصُّبْحَ ثُمَّ يُقِيمُ بِالْأَرْضِ  

[Machine] Ibn Umar used to give the call to prayer while on his mount, and it was narrated that there is a hadith in this regard which is considered to be "mursal."  

أَنَّ ابْنَ عُمَرَ كَانَ يُؤَذِّنُ عَلَى رَاحِلَتِهِ وَرُوِي فِيهِ حَدِيثٌ مُرْسَلٌ  

[Machine] The Messenger of Allah ﷺ ordered Bilal to make the call to prayer while on a journey. They then stopped and performed two units of prayer, two units of prayer. Then the Prophet ﷺ stood up and led them in the morning prayer.  

أَنَّ رَسُولَ اللهِ ﷺ أَمَرَ بِلَالًا فِي سَفَرٍ فَأَذَّنَ عَلَى رَاحِلَتِهِ ثُمَّ نَزَلُوا فَصَلَّوْا رَكْعَتَيْنِ رَكْعَتَيْنِ ثُمَّ أَمَرَهُ فَأَقَامَ فَصَلَّى بِهِمُ الصُّبْحَ  

[Machine] I entered upon Abu Zaid Al-Ansari, and he gave the call to prayer and established it while he was sitting. He said, "A man came forward and led us in prayer, and he was lame, having been injured in the cause of Allah the Exalted." And it has been narrated to us from Ata ibn Abi Rabah that he said, "It is disliked for someone sitting to give the call to prayer unless he has an excuse."  

دَخَلْتُ عَلَى أَبِي زَيْدٍ الْأَنْصَارِيِّ فَأَذَّنَ وَأَقَامَ وَهُوَ جَالِسٌ قَالَ وَتَقَدَّمَ رَجُلٌ فَصَلَّى بِنَا وَكَانَ أَعْرَجَ أُصِيبَ رِجْلُهُ فِي سَبِيلِ اللهِ تَعَالَى وَرُوِّينَا عَنْ عَطَاءِ بْنِ أَبِي رَبَاحٍ أَنَّهُ قَالَ يُكْرَهُ أَنْ يُؤَذِّنَ قَاعِدًا إِلَّا مِنْ عُذْرٍ