Abu Dawud Book 8, Hadith Number 2534.

Narated By Sahl ibn Sa’d : The Prophet (PBUH) said: Two (prayers) are not rejected, or seldom rejected: Prayer at the time of the call to prayer, and (the prayer) at the time of fighting, when the people grapple with each other. Musa said: Rizq ibn Sa’id ibn AbdurRahman reported from AbuHazim on the authority of Sahl ibn Sa’d from the Prophet (PBUH) as saying: And while it is raining.