Anas said that when they experienced a drought ‘Umar b. al-Khattab prayed for rain by virtue of al-‘Abbas b. ‘Abd al-Muttalib, and said, "O God, we used to supplicate You by virtue of our prophet and You didst give us water. We are now supplicating You by virtue of our prophet’s uncle, so give us water.” He said that they were then given water. Bukhari transmitted it.

وَعَنْ أَنَسٍ أَنَّ عُمَرَ بْنَ الْخَطَّابِ كَانَ إِذْ قحطوا استسقى بالبعاس بْنِ عَبْدِ الْمُطَّلِبِ فَقَالَ: اللَّهُمَّ إِنَّا كُنَّا نَتَوَسَّلُ إِلَيْكَ بِنَبِيِّنَا فَتَسْقِينَا وَإِنَّا نَتَوَسَّلُ إِلَيْكَ بِعَمِّ نَبِيِّنَا فَاسْقِنَا. قَالَ: فَيُسْقَوْنَ. رَوَاهُ الْبُخَارِيُّ