Al-Mu'jam al-Awsat 7450 — he heard the Messenger of Allah ﷺ say: Allah

It is narrated from Sayyiduna Abu Umamah al-Bahili (may Allah be pleased with him) that he heard the Messenger of Allah (peace and blessings be upon him) say: "Allah has made the fasting of Ramadan obligatory upon you, and He has not made its night prayer (the Tarawih prayer) obligatory upon you. Its night prayer is only something that you yourselves have begun, so persist in it; for some people of the Children of Israel introduced an innovation and Allah blamed them for abandoning it, and He said: 'And monasticism, which they innovated; We did not prescribe it for them, (they did it) only seeking the pleasure of Allah, but they did not observe it as it ought to be observed' - to the end of the verse."
Imam al-Tabarani (may Allah have mercy on him) said: "This hadith is not narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) except with this chain; Isma'il bin Amr is alone in narrating it."