Which is more rewarding: studying at night with the intention of performing Qiyam al-Layl, or sleeping after 'Isha and applying the Sunnah, then studying after Fajr, with a consistent portion of Qiyam al-Layl in both cases?

The Prophet (peace be upon him) disliked sleeping before 'Isha and conversing after it. However, studying beneficial knowledge does not fall under this prohibition. The dislike of conversing after 'Isha is specific to instances where the conversation is not about a desired matter. The wisdom behind this is to prevent it from becoming a reason for abandoning night prayers or oversleeping and missing the Fajr prayer. Therefore, studying after the 'Isha prayer is preferable due to the reward and recompense it entails, especially if it does not prevent one from performing night prayers and the obligatory Fajr prayer on time. And speaking out of necessity or for good, such as reading the Prophet's hadith, studying fiqh, narrating stories of the righteous, and conversing with a guest, is not disliked.