Jami` at-Tirmidhi Hadith 3473

The Messenger of Allah (ﷺ) said: “Whoever says ten times: ‘I bear witness that none has the right to be worshipped but Allah. Alone, without partner, One Deity, the One, As-Samad, He did not take a wife, nor a child, nor is there anyone like Him, (Ash-hadu an lā ilāha illallāh, waḥdahu lā sharīka lahu, ilahan wahidan, aḥadan ṣamadan lam yattakhidh ṣāḥibatan wa lā waladan wa lam yakun lahu kufuwan aḥad)’ Allah will write for him forty million good deeds.”