What is the ruling on praying after Asr or after Fajr, even if it is a prayer for rain (Salat al-Istisqa') after Asr?

Voluntary prayers are prohibited after Fajr prayer and after Asr prayer. However, prayers with a specific reason, such as Tahiyyat al-Masjid (greeting the mosque) and Sunnat al-Wudu' (prayer after ablution), are permissible during times of prohibition. The Shafi'is differed on the permissibility of Salatul-Istisqa' (prayer for rain) during times of prohibition, given that it has a reason, and most of them held it to be permissible. Al-Nawawi said: "As for prayers that have a reason, there is no reprehensibility in them." He mentioned that the Khurasanis differed concerning Salatul-Istisqa', and the soundest opinion is that it is not reprehensible. Ibn Qasim preferred the permissibility of performing Salatul-Istisqa' during times of prohibition if there is a pressing need for it, because the harm of missing it outweighs the harm of resemblance (to the times of sun-worship).