The Prophet (ﷺ) said, " Two (du'aa's) are not rejected, Prayer (du'aa) at the time of the call to prayer (Adhan), and (du'aa) while it is Raining."
(Abu Dawood 2540, Al-Haakim in al-Mustadrak 2534, At-Tabaraani in Mu'jam al-kabeer 5756, Grade : Sahih by Al-Albaani in Sahih al- Jaami 3078)