Was Abu Bakr Al-Siddiq performing Qunut in all of his prayers or some of them during the apostasy wars, reciting, "Our Lord, let not our hearts deviate after You have guided us," and is this considered Qunut Al-Nawazil (Qunut for calamities)?

What is narrated from Abu Bakr Al-Siddiq, may Allah be pleased with him, is that he recited the verse: {Our Lord, let not our hearts deviate after You have guided us and grant us from Yourself mercy. Indeed, You are the Bestower} in the third rak'ah of the Maghrib prayer only, not in all prayers. Scholars have interpreted this narration to mean that it was a form of supplication (du'a) and qunut, not a recitation. It is possible that Abu Bakr supplicated with it at the end of the rak'ah with the intention of du'a, due to a memory or a state of reverence that he experienced, not intending to combine its recitation with the recitation of Umm al-Qur'an (Surat Al-Fatihah). Some scholars believe that it is not sunnah to add to the recitation of Umm al-Kitab (Surat Al-Fatihah) in the last two rak'ahs, and that what Al-Siddiq did was intended as a supplication, not a recitation, in order to conform to the action of the Prophet, peace and blessings be upon him. Ahmad held the view that it is permissible to supplicate with this verse in prayer. Supplicating with this verse is not part of qunut an-nawazil (qunut for calamities), because it does not involve a supplication for the removal of a calamity.