When is combining prayers due to rain permissible regarding the timing of the first prayer?

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Combining prayers due to rain must occur at the time of the first prayer, following the practice of the Pious Predecessors (Salaf). Delaying the first prayer until the time of the second prayer is prohibited because it leads to hardship, necessitates being out in the darkness, or requires prolonged waiting in the mosque until the time of Isha prayer enters. Furthermore, since people customarily gather for Maghrib, keeping them in the mosque to combine prayers is more burdensome than offering each prayer at its appointed time. Additionally, the need for combination might cease before the time for the first prayer expires, invalidating the combination and making it impermissible.