The Quran

سَيَقولُ المُخَلَّفونَ إِذَا انطَلَقتُم إِلىٰ مَغانِمَ لِتَأخُذوها ذَرونا نَتَّبِعكُم ۖ يُريدونَ أَن يُبَدِّلوا كَلامَ اللَّهِ ۚ قُل لَن تَتَّبِعونا كَذٰلِكُم قالَ اللَّهُ مِن قَبلُ ۖ فَسَيَقولونَ بَل تَحسُدونَنا ۚ بَل كانوا لا يَفقَهونَ إِلّا قَليلًا

Muhammad Asad

As soon as you [O believers] are about to set forth on a war that promises booty,¹ those who stayed behind [aforetime] will surely say, "Allow us to go with you" - [thus showing that] they would like to alter the Word of God.² Say: "By no means shall you go with us: God has declared aforetime³ [to whom all spoils shall belong]." Thereupon they will [surely] answer, "Nay, but you begrudge us [our share of booty]!" Nay, they can grasp but so little of the truth!

Lit., "set forth to take booty": i.e., any expedition other than against the Quraysh of Mecca, with whom the Prophet had just concluded a truce. This is generally taken as an allusion to the forthcoming war against the Jews of Khaybar (in the year 7 H.), but the meaning may well be more general.
Evidently a reference to 8:1 - "All spoils of war belong to God and the Apostle" - which, as pointed out in note 1 on that verse, implies that no individual warrior can have any claim to the booty obtained in war. Moreover, fighting for the sake of booty contravenes the very principle of a "war in God's cause", which may be waged only in defence of faith or liberty (cf. surah 2, note 167), "until there is no more oppression and all worship is devoted to God alone" (see 2:193 and the corresponding note 170). It is to these principles, too, that the Prophet's anticipated answer, mentioned in the sequence, refers.
I.e., in the first verse of Al-Anfal, which was revealed in the year 2 H. (see preceding note).