Imām Ibnu ʾUthaymīn (حفظه الله) said that on the Day of Judgement,

“…people will have grievances towards one another, and surely it will be deducted from their good deeds except from the fast (ṣawm), for surely nothing will be taken from it because it is (done) for Allāh (عزّ وجلّ) and not for people. And this is a good interpretation that the reward of fasting is saved for it’s keeper, and nothing is taken from it due the grievances against others.”

Source: Explanation of Riyāḍ aṣ-Ṣāliḥīn Vol. 3 Pg. 482

Translated by Zubayr Abbasi