ENOfficial
Ibn 'Abbas said God’s Messenger went out (i.e. to pray for rain) wearing old clothes, with a humble and lowly manner, making petition. Tirmidhi, Abu Dawud, Nasa’i and Ibn Majah transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنِ ابْنِ عَبَّاسٍ قَالَ: خَرَجَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَعْنِي فِي الِاسْتِسْقَاءِ مُتَبَذِّلًا مُتَوَاضِعًا مُتَخَشِّعًا مُتَضَرِّعًا. رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُدَ وَالنَّسَائِيُّ وَابْنُ مَاجَهْ
sunnah.com