(I said;Ask forgiveness from your Lord, verily, He is Oft-Forgiving; He will send rain to you Midrar,
meaning, continuous rain.
Thus, it is recommended to recite this Surah in the prayer for rain due to this Ayah.
This has been reported from the Commander of the faithful, `Umar bin Al-Khattab. He ascended the Minbar to perform the prayer for rain, and he did not do more than seeking Allah's forgiveness and reciting the Ayat that mention seeking Allah's forgiveness. Among these Ayat;
فَقُلْتُ اسْتَغْفِرُوا رَبَّكُمْ إِنَّهُ كَانَ غَفَّارًا
يُرْسِلِ السَّمَاء عَلَيْكُم مِّدْرَارًا
I said;Ask forgiveness from your Lord, verily, He is Oft-Forgiving; He will send rain to you Midrar,
Then he (`Umar) said, "Verily, I have sought rain with the keys of the sky which cause the rain to descend."
Ibn `Abbas and others have said,
"It (Midrar) means some of it (rain) following others."
Concerning Allah's statement,
وَيُمْدِدْكُمْ بِأَمْوَالٍ وَبَنِينَ وَيَجْعَل لَّكُمْ جَنَّاتٍ وَيَجْعَل لَّكُمْ أَنْهَارًا