Is it permissible to pray Salatul-Istikhara after Fajr or Asr prayer, and what is the reason for its impermissibility if it is not permissible?

The four schools of thought (madhahib) prohibit Istikhara prayer during disliked times. The Shafi'is stipulate that the reason for the prayer must precede it, while the reason for Istikhara comes after it. As for the Hanbalis, Hanafis, and Malikis, they prohibit it due to the general prohibition.