Musnad Ahmad 1304:53

'Abd al-Samad narrated to us, Hammad narrated to us, from Thabit, from Shahr ibn Hawshab, from Asma', that she heard the Prophet, peace and blessings of Allah be upon him, reciting: "Indeed, Allah forgives all sins," and He does not care, "Indeed, it is He who is the Forgiving, the Merciful."