Revelation 7:10-17: "10 and crying out with a loud voice, 'Salvation belongs to our God who sits on the throne, and to the Lamb!' 11 And all the angels were standing around the throne and around the elders and the four living creatures, and they fell on their faces before the throne and worshiped God, 12 saying, 'Amen! Blessing and glory and wisdom and thanksgiving and honor and power and might be to our God forever and ever! Amen.'
"13 Then one of the elders addressed me, saying, 'Who are these, clothed in white robes, and from where have they come?' 14 I said to him, 'Sir, you know.' And he said to me, 'These are the ones coming out of the great tribulation. They have washed their robes and made them white in the blood of the Lamb.
"15 'Therefore they are before the throne of God, and serve him day and night in his temple; and he who sits on the throne will shelter them with his presence. 16 They shall hunger no more, neither thirst anymore; the sun shall not strike them, nor any scorching heat. 17 For the Lamb in the midst of the throne will be their shepherd, and he will guide them to springs of living water, and God will wipe away every tear from their eyes.'"
Revelation 21:2-7: "2 And I saw the holy city, new Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband. 3 And I heard a loud voice from the throne saying, 'Behold, the dwelling place of God is with man. He will dwell with them, and they will be his people, and God himself will be with them as their God. 4 He will wipe away every tear from their eyes, and death shall be no more, neither shall there be mourning, nor crying, nor pain anymore, for the former things have passed away.'
"5 And he who was seated on the throne said, 'Behold, I am making all things new.' Also he said, 'Write this down, for these words are trustworthy and true.' 6 And he said to me, 'It is done! I am the Alpha and the Omega, the beginning and the end. To the thirsty I will give from the spring of water of life without payment. 7 The one who conquers will have this heritage, and I will be his God and he will be my son."
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The text is public domain:
Oh, what their joy and their glory must be,Those endless Sabbaths the blessed ones see!Crowns for the valiant, to weary ones rest;God shall be all, and in all ever blest.In new Jerusalem joy shall be found,Blessings of peace shall forever abound;Wish and fulfillment are not severed there,Nor the things prayed for come short of the prayer.We, where no trouble distraction can bring,Safely the anthems of Zion shall sing;While for Your grace, Lord, their voices of praiseYour blessed people shall evermore raise.Now let us worship our Lord and our King,Joyfully raising our voices to sing:Praise to the Father, and praise to the Son,Praise to the Spirit, to God, Three in One.
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The first two verses come from the passage from Revelation 21, and the last two verses come from the passage from Revelation 7, although while the hymn emphasizes singing, the text from Revelation 7 has "crying out with a loud voice" and "saying."
The line "Crowns for the valiant, to weary ones rest" in the first verse seems to have specific Biblical sources too: "Crowns for the valiant" from either James 1:12 ("when he has stood the test he will receive the crown of life, which God has promised to those who love him") or Revelation 2:10 ("'Be faithful unto death, and I will give you the crown of life.'") and "to weary ones rest" from Matthew 11:28 ("'Come to me, all who labor and are heavy laden, and I will give you rest.'").
