Islam is the complete religion is mentioned in Surah 5 Al-Ma’idah, Ayat 3-3: 

(5:3) Forbidden to you are carrion,⁹ blood, the flesh of swine, the animal slaughtered in any name other than Allah’s,¹⁰ the animal which has either been strangled, killed by blows, has died of a fall, by goring or that devoured by a beast of prey – unless it be that which you yourselves might have slaughtered while it was still alive¹¹ – and that which was slaughtered at the altars.¹²–¹³ You are also forbidden to seek knowledge of your fate by divining arrows.¹⁴ All these are sinful acts. This day the unbelievers have fully despaired of your religion. Do not fear them; but fear Me.¹⁵ This day I have perfected for you your religion, and have bestowed upon you My bounty in full measure, and have been pleased to assign for you Islam as your religion. (Follow, then, the lawful and unlawful bounds enjoined upon you.)¹⁶ As for he who is driven by hunger, without being wilfully inclined to sin, surely Allah is All-Forgiving, All-Compassionate.¹⁷