Kitāb al-Zuhd

Hadith 38
sincerity
وعنه عليه السلام قال: من أوثق عرى الايمان أن تحب لله وتبغض لله وتعطى في الله وتمنع في الله
12.Also [narrated] from him (a), that he said, “Among the firmest handles of faith are that you love for Allah, hate for Allah, give for Allah, and withhold for Allah.”
Source: Ḥusayn b. Saʿīd al-Ahwāzī