Is it permissible to pray behind one's husband as an imam in Qiyam al-Layl (night prayers), given his frequent yawning and the unclearness of the verses he recites due to overwhelming drowsiness?

If a man wakes up at night and wakes his wife, and they pray two rak'ahs, they will be recorded among those men and women who remember Allah much. If a person prays while feeling drowsy, it is better for him to stop praying until the drowsiness leaves him, as the Prophet, peace and blessings be upon him, said: "If any of you feels drowsy while praying, he should lie down until sleep leaves him." The worshipper is required to approach his prayer with humility and a focused heart.