What is the ruling on a worshiper's thoughts in the night vigil prayer (Qiyam al-Layl) preparing him to remember the grave and the Day of Resurrection when prolonging the bowing (ruku'), and does the absence of this preparation affect the devoutness (khushu') in prayer?

What you feel during prayer is an indication of the presence of the heart and submissiveness (khushu'), and this is a great blessing. Remembering matters of the afterlife helps in achieving this. The Prophet, peace and blessings be upon him, said: "Remember death in your prayer, for if a man remembers death in his prayer, he is most likely to perfect his prayer." He also said: "When you stand for your prayer, pray the prayer of one who is bidding farewell."