Riyad as-Salihin

Abu Hurairah (May Allah bepleased with him) reported: Messenger of Allah (ﷺ) said, "There are three signs of a hypocrite: When he speaks, he lies; when he makes a promise, he breaks it; and when he is trusted, he betrays his trust."

[Al-Bukhari and Muslim].

Another narration adds the words: 'Even if he observes fasts, performs Salat and asserts that he is a Muslim".