Allāhumma ‘asqinā ghaythan mughīthan marī'an murī`a, nāfi`an ghayra ḍārr, `ājilan ghayra ājil. O Allah, shower upon us abundant rain, beneficial not harmful, swiftly and not delayed. Reference: Abu Dawud 1/303. See also Al-Albani SahihAbu Dawud 1/216.