أَخْبَرَنَا إِسْحَاقُ بْنُ مَنْصُورٍ، وَمُحَمَّدُ بْنُ الْمُثَنَّى، عَنْ عَبْدِ الرَّحْمَنِ، عَنْ سُفْيَانَ، عَنْ هِشَامِ بْنِ إِسْحَاقَ بْنِ عَبْدِ اللَّهِ بْنِ كِنَانَةَ، عَنْ أَبِيهِ، قَالَ أَرْسَلَنِي فُلاَنٌ إِلَى ابْنِ عَبَّاسٍ أَسْأَلُهُ عَنْ صَلاَةِ، رَسُولِ اللَّهِ صلى الله عليه وسلم فِي الاِسْتِسْقَاءِ فَقَالَ خَرَجَ رَسُولُ اللَّهِ صلى الله عليه وسلم مُتَضَرِّعًا مُتَوَاضِعًا مُتَبَذِّلاً فَلَمْ يَخْطُبْ نَحْوَ خُطْبَتِكُمْ هَذِهِ فَصَلَّى رَكْعَتَيْنِ ‏.‏

It was narrated from Hisham bin Ishaq bin Abdullah bin Kinanah that : His father said: "So and so sent me to ask him how the Messenger of Allah (PBUH) prayed for rain (Istisqa')." He said: 'The Messenger of Allah (PBUH) went out beseeching and humble, (dressed) in a state of humility. He did not give a Khutbah like this Khutbah of yours, and he prayed two rak'ahs.'" Translation Not Available

Book reference: Sunan An Nisai Book 17 Hadith 1506
Web reference: Sunan An Nisai Volume 2 Book 17 Hadith 1507