It is reported that Ayyûb Al-Sakhtiyânî – Allâh have mercy on him – said:

Whoever loves Abû Bakr has upheld the religion, whoever loves ‘Umar has made the way clear, whoever loves ‘Uthmân is enlightened by the light of Allâh, and whoever loves ‘Alî has taken the firmest handhold. Whoever speaks well of the Companions of Allâh’s Messenger – Allâh’s peace and blessings be upon him – is clear of hypocrisy (nifâq), but whoever belittles any one of them or dislikes [any one of them] for something he did, then he is a heretic (mubtadi’), an opponent of the Sunnah and the Righteous Predecessors (the Salaf), and it is feared that none of his deeds will be raised to the heavens until he loves all of [the Companions] and his heart is clear towards them.

Ibn Abî Zamanîn, Usûl Al-Sunnah article 189.