Abu Wajzah al-Sa'di narrates from his father that he said: Sayyiduna Umar (may Allah be pleased with him) went out to supplicate for rain, and he did nothing more than seek forgiveness. I said: Why does he not speak about what he came out for? I did not know that seeking rain is seeking forgiveness; then we were given rain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6422