Bayhaqi 3096 — Qunut in the prayers when a calamity befalls

(a) Humayd al-Tawil narrates from Sayyiduna Anas (may Allah be pleased with him) that young men of the Ansar would listen attentively to the Qur'an, then withdraw to a corner of Madinah; their families would think they were in the mosque, and the people of the mosque would think they were at home. They would pray through the night until, when the morning drew near, some of them would go to gather firewood and some would go to fetch fresh water. Then they would come back and place their bundles and water-skins at the doors of the chambers of the Messenger of Allah (peace and blessings be upon him). The Prophet (peace and blessings be upon him) sent them to Bi'r Ma'unah, and there they were all martyred. After that, the Messenger of Allah (peace and blessings be upon him) supplicated against their killers for fifteen nights.
(b) Likewise, Alqamah bin Abi Alqamah narrated it from Sayyiduna Anas (may Allah be pleased with him). In it he says that the Messenger (peace and blessings be upon him) supplicated against their killers for fifteen days.
(c) Likewise, Ja'far bin Muhammad also transmitted a mursal narration from his father, which mentions fifteen days.
(d) However, the narrations of one month are more famous, clearer and more authentic. 'Wallahu a'lam' (And Allah knows best). Most of the narrations from Sayyiduna Anas (may Allah be pleased with him) establish qunut in the morning prayer, and likewise it is established from Sayyiduna Anas (may Allah be pleased with him) in the Maghrib prayer as well.