‘Umar (ra) said, “By He in whose hand is my soul, if Abū Bakr had obeyed us, we would have committed kufr in a single morning, and that was when they asked him to go easy concerning zakāh [by not waging war against the apostates over it], but he refused. He said, ‘If they were to withhold from me a short rope, I would wage jihād against them over it.’” [Musannaf Ibn Abī Shaybah]
He (ra) also said, “We almost committed kufr in a single morning if not that Allah saved us through Abū Bakr as-Siddīq (ra).” [Al-Ibānah al-Kubrā]
Abū Rajā’ al-‘Utāridī said, “I entered al-Madīnah and saw the people gathered around a man kissing the head of another while the kisser was saying, ‘May I be killed in your defense! If not for you, we would have been ruined.’ So I asked, ‘Who is the kisser and who is the one being kissed?’ They said, ‘That is ‘Umar kissing Abū Bakr’s head for his war against the people of apostasy who resisted zakāh.” [Tārīkh Dimashq]
Abū Hurayrah (ra) said, “By He other than whom there is no god, if Abū Bakr had not been appointed khalīfah, Allah would not be worshipped on the Earth!” He repeated this three times. [Al-I’tqād – al-Bayhaqī]
Wakī’ Ibn al-Jarrāh said, “If not for Abū Bakr, Islam would have perished.” [Al-Ibānah al-Kubrā]