Musannaf Ibn Abi Shaybah 32429 — Book of Faith

Mughirah (may Allah have mercy on him) said: Ibrahim (may Allah have mercy on him) was asked about a man who asks another man: "Are you a believer?" He (may Allah have mercy on him) said: "Answering it is an innovation (bid'ah), and I am not pleased to say that I have doubt in my faith."