The Prophet ﷺ 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 ﷺ as saying: And while it is raining. (Using translation from Abū Dāʾūd 2540)   

قَالَ رَسُولُ اللهِ ﷺ ثِنْتَانِ لَا تُرَدَّانِ أَوْ قَلَّمَا تُرَدَّانِ؛ الدُّعَاءُ عِنْدَ النِّدَاءِ عِنْدَ الْبَأْسِ حِينَ يُلْحِمُ بَعْضُهُمْ بَعْضًا قَالَ مُوسَى وَحَدَّثَنِي رِزْقُ بْنُ سَعِيدِ بْنِ عَبْدِ الرَّحْمَنِ الْمَدَنِيُّ عَنْ أَبِي حَازِمٍ عَنْ سَهْلِ بْنِ سَعْدٍ عَنِ النَّبِيِّ ﷺ قَالَ وَتَحْتَ الْمَطَرِ وَرُوِيَ فِي ذَلِكَ عَنْ أَبِي أُمَامَةَ عَنِ النَّبِيِّ ﷺ إِلَّا أَنَّ عُفَيْرَ بْنَ مَعْدَانَ عَلَى طَرِيقَةٍ  

[Machine] "From the Messenger of Allah ﷺ, who said: The doors of the heavens are opened, and supplications are answered at four specific times: when the rows of prayer are aligned, when rain falls, during the establishment of prayer, and when the Kaaba is seen."  

عَنْ رَسُولِ اللهِ ﷺ قَالَ تُفْتَحُ أَبْوَابُ السَّمَاءِ وَيُسْتَجَابُ الدُّعَاءُ فِي أَرْبَعَةِ مَوَاطِنَ عِنْدَ الْتِقَاءِ الصُّفُوفِ وَعِنْدَ نُزُولِ الْغَيْثِ وَعِنْدَ إِقَامَةِ الصَّلَاةِ وَعِنْدَ رُؤْيَةِ الْكَعْبَةِ