Narrated Abdullah ibn Abbas:

Ishaq ibn Abdullah ibn Kinanah reported: Al-Walid ibn Utbah or (according to the version of Uthman) al-Walid ibn Uqbah, the then governor of Medina, sent me to Ibn Abbas to ask him about the prayer for rain offered by the Messenger of Allah ﷺ. He said: The Messenger of Allah ﷺ went out wearing old clothes in a humble and lowly manner until he reached the place of prayer. He then ascended the pulpit, but he did not deliver the sermon as you deliver (usually). He remained engaged in making supplication, showing humbleness (to Allah) and uttering the takbir (Allah is most great). He then offered two rak'ahs of prayer as done on the 'Id (festival).

Abu Dawud said: This is the version of al-Nufail. What is correct is Ibn Utbah's

حَدَّثَنَا النُّفَيْلِيُّ، وَعُثْمَانُ بْنُ أَبِي شَيْبَةَ، نَحْوَهُ قَالاَ حَدَّثَنَا حَاتِمُ بْنُ إِسْمَاعِيلَ، حَدَّثَنَا هِشَامُ بْنُ إِسْحَاقَ بْنِ عَبْدِ اللَّهِ بْنِ كِنَانَةَ، قَالَ أَخْبَرَنِي أَبِي قَالَ، أَرْسَلَنِي الْوَلِيدُ بْنُ عُتْبَةَ - قَالَ عُثْمَانُ ابْنُ عُقْبَةَ وَكَانَ أَمِيرَ الْمَدِينَةِ - إِلَى ابْنِ عَبَّاسٍ أَسْأَلُهُ عَنْ صَلاَةِ، رَسُولِ اللَّهِ ﷺ فِي الاِسْتِسْقَاءِ فَقَالَ خَرَجَ رَسُولُ اللَّهِ ﷺ مُتَبَذِّلاً مُتَوَاضِعًا مُتَضَرِّعًا حَتَّى أَتَى الْمُصَلَّى - زَادَ عُثْمَانُ فَرَقِيَ عَلَى الْمِنْبَرِ ثُمَّ اتَّفَقَا - وَلَمْ يَخْطُبْ خُطَبَكُمْ هَذِهِ وَلَكِنْ لَمْ يَزَلْ فِي الدُّعَاءِ وَالتَّضَرُّعِ وَالتَّكْبِيرِ ثُمَّ صَلَّى رَكْعَتَيْنِ كَمَا يُصَلِّي فِي الْعِيدِ . قَالَ أَبُو دَاوُدَ وَالإِخْبَارُ لِلنُّفَيْلِيِّ وَالصَّوَابُ ابْنُ عُتْبَةَ .