Musannaf Ibn Abi Shayba 7:428

Sharīk narrated to us, from Mughīrah, from Ibrāhīm; and from Ibn Abī Khālid, from ‘Āmir, regarding the one who breaks his fast for a day in Ramaḍān: He said: He should seek forgiveness from Allah and repent to Him, and he should not repeat it, and he should make up a day in its place.