They were with the Prophet (S) on a journey. They wound up in a narrow area when Salat became due. Then it began raining from the sky above them, and it was wet beneath them. So Messenger of Allah (S) called the Adhan while he was on his mount, and then the Iqamah, going forward on his mount. He let them in Salat by making gestures, making his prostrations lower than his bowing.  

عَنْ جَدِّهِ أَنَّهُمْ كَانُوا مَعَ النَّبِيِّ ﷺ فِي مَسِيرٍ فَانْتَهَوْا إِلَى مَضِيقٍ وَحَضَرَتِ الصَّلاَةُ فَمُطِرُوا السَّمَاءُ مِنْ فَوْقِهِمْ وَالْبِلَّةُ مِنْ أَسْفَلَ مِنْهُمْ فَأَذَّنَ رَسُولُ اللَّهِ ﷺ وَهُوَ عَلَى رَاحِلَتِهِ وَأَقَامَ أَوْ أَقَامَ فَتَقَدَّمَ عَلَى رَاحِلَتِهِ فَصَلَّى بِهِمْ يُومِئُ إِيمَاءً يَجْعَلُ السُّجُودَ أَخْفَضَ مِنَ الرُّكُوعِ