Majma al-Zawaid — Hadith 11318

Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates concerning this saying of Allah Almighty: (Allah Almighty says:) "The Forgiver of sin, the Acceptor of repentance, Severe in punishment, the Possessor of abundance; there is no god but He; to Him is the return." Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: Here "the Forgiver of sin" means that He will forgive the sin of the one who says "La ilaha illallah (There is no god but Allah)"; and "the Acceptor of repentance" is for the one who says: There is no god but Allah; and "Severe in punishment" is for the one who does not say "La ilaha illallah"; and "Dhi al-tawl" means that He is the Possessor of abundance; "there is no god but He", because the disbelievers of Quraysh did not acknowledge His oneness, so He Himself declared His oneness; "to Him is the return", that is, the one who says "La ilaha illallah" will return to Him and Allah Almighty will admit him into Paradise, and the one who does not say "La ilaha illallah" will also return to Him and Allah Almighty will admit him into Hell.
Al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains Yahya bin Abd al-Hamid al-Himmani, who is da'if (weak).