The Quran

وَما لَكُم أَلّا تُنفِقوا في سَبيلِ اللَّهِ وَلِلَّهِ ميراثُ السَّماواتِ وَالأَرضِ ۚ لا يَستَوي مِنكُم مَن أَنفَقَ مِن قَبلِ الفَتحِ وَقاتَلَ ۚ أُولٰئِكَ أَعظَمُ دَرَجَةً مِنَ الَّذينَ أَنفَقوا مِن بَعدُ وَقاتَلوا ۚ وَكُلًّا وَعَدَ اللَّهُ الحُسنىٰ ۚ وَاللَّهُ بِما تَعمَلونَ خَبيرٌ

Muhammad Asad

And why should you not spend freely in the cause of God, seeing that God's [alone] is the heritage of the heavens and the earth?¹ Not equal are those of you who spent and fought [in God's cause] before the Victory² [and those who did not do so]: they are of a higher rank than those who would spend and fight [only] after it - although God has promised the ultimate good to all [who strive in His cause].³ And God is aware of all that you do.

I.e., "that to God belongs all that is ...", etc.: see note 5 above; also note 22 on 15:23.
I.e., before the conquest of Mecca in 8 H., when the Muslims were still weak and their future uncertain.
The above principle applies, of course, to the relative merits of believers of all times who strive in God's cause before andlor after success has been achieved.