Musannaf Ibn Abi Shaybah

Hazrat Abu Hazim narrates that Hazrat Sahl bin Sa’d Sa’idi said: There are two moments when the gates of the heavens are opened, and it is very rare that the supplication of the one who prays is returned to him unanswered: at the time of the call to prayer for Salah, and at the time of forming ranks for Jihad in the path of Allah.