Matthew 4:4- ὁ δὲ ἀποκριθεὶς εἶπεν Γέγραπται Οὐκ ἐπ' ἄρτῳ μόνῳ ζήσεται ὁ ἄνθρωπος, ἀλλ' ἐπὶ παντὶ ῥήματι ἐκπορευομένῳ διὰ στόματος θεοῦ.
Deuteronomy 8:3-καὶ ἐκάκωσέν σε καὶ ἐλιμαγχόνησέν σε καὶ ἐψώμισέν σε τὸ μαννα ὃ οὐκ εἴδησαν οἱ πατέρες σου ἵνα ἀναγγείλῃ σοι ὅτι οὐκ ἐπ᾽ ἄρτῳ μόνῳ ζήσεται ὁ ἄνθρωπος ἀλλ᾽ ἐπὶ παντὶ ῥήματι τῷ ἐκπορευομένῳ διὰ στόματος θεοῦ ζήσεται ὁ ἄνθρωπος
According to Matthew's account, Christ quotes the part of Deut. 8:3 that is relevant for his purpose. Notice how closely his wording mirrors the passage from Deuteronomy.
David L. Turner supplies these observations from the Baker Exegetical Commentary on Matthew:
Jesus’s response simply cites the second half of Deut. 8:3 with an introductory formula that stresses the abiding authority of the Hebrew Bible: “It is written” (NLT: “The Scriptures say”). In context, this passage rehearses God’s care for Israel during its forty-year wilderness experience. The first half of Deut. 8:3 alludes to God’s purpose in permitting Israel’s hunger in the wilderness: it was so that the people might learn that they needed not only bread but also God’s word to survive (cf. John 4:34; 6:35). This purpose of God in Deut. 8:3 is similar to the statement of purpose in Matt. 4:1. Deuteronomy 8:5 likens the wilderness wandering to a father’s discipline, and this terminology finds its full implications in the testing of Jesus. Satanic temptation is the setting for divine testing, and Jesus no doubt recalls the earlier test, which was not passed with flying colors. He is aware of the daily need to depend on the Father for bread (Matt. 7:9), and he will not use his power as some sort of magician.