Majma al-Zawaid — Hadith 16923

In one narration the words are: "And 'Say: He is Allah, the One'" (that is, whoever recites Ayat al-Kursi and Surah al-Ikhlas after every prayer, nothing will stand between him and entering Paradise except death).
Al-Tabarani recorded it in al-Mu'jam al-Kabir and al-Mu'jam al-Awsat with various chains, one of which is jayyid (good).