Anas bin Malik reported,

Whenever they suffered drought, Umar bin Khattab would seek rain through Abbas bin Abdul-Muttalib. He would say, "O Allah, we used to seek means to You through our Prophet and You would give us rain. Now we seek means to You through the uncle of our Prophet, so give us rain." And they would be given rain.

Azami 10974

Sahih

عن أنس

أن عمر بن الخطاب كان إذا قحطوا استسقى بالعباس بن عبد المطلب، فقال اللهم إنا كنا نتوسل إليك بنبينا فتسقينا، وإنا نتوسل إليك بعم نبينا فاسقنا، قال: فيسقون.

الأعظمي 10974صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Supplications, remembrances, and prayer upon the chosen Prophet ﷺ
Chapter
Legitimate means of seeking nearness in supplication
Section
Seeking means to Allah through the supplication of a living righteous man
Numbering
Jami al-Kamil 10974 (2nd edition)