Al-Matalib al-'Aliyah 743 — The fear prayer

It is narrated from Sayyiduna Hudhayfah (may Allah be pleased with him) that he said: "The prayer of fear (salat al-khawf) is two rak'ahs and four prostrations; and if some sudden matter or a surprise attack of the enemy compels the one praying to hurry, then in such an emergency it becomes permissible to fight the enemy and to speak as needed during the prayer."
Imam Abu Dawud recorded it; the narrator Sharik bin Abdullah al-Qadi in its chain is open to question among the hadith scholars because of his memory. However, among the jurists there is scholarly discussion of such latitude in the rulings of salat al-mutaradah (praying while running or fighting) in a state of extreme fear.