Which day is this referring to?

Malachi 4:1 For, behold, the day cometh, that shall burn as an oven; and all the proud, yea, and all that do wickedly, shall be stubble: and the day that cometh shall burn them up, saith the LORD of hosts, that it shall leave them neither root nor branch.

Is it speaking of the day of the 6th trumpet?

Revelation 9:17 And thus I saw the horses in the vision, and them that sat on them, having breastplates of fire, and of jacinth, and brimstone: and the heads of the horses were as the heads of lions; and out of their mouths issued fire and smoke and brimstone.

  18 By these three was the third part of men killed, by the fire, and by the smoke, and by the brimstone, which issued out of their mouths.

Or is it referring to the day of the 4th vial?

Revelation 16:8 And the fourth angel poured out his vial upon the sun; and power was given unto him to scorch men with fire.

  9 And men were scorched with great heat, and blasphemed the name of God, which hath power over these plagues: and they repented not to give him glory.

Or is it speaking of the day of Mystery, Babylon's destruction?

Revelation 17:16 And the ten horns which thou sawest upon the beast, these shall hate the whore, and shall make her desolate and naked, and shall eat her flesh, and burn her with fire.

Revelation 18:8 Therefore shall her plagues come in one day, death, and mourning, and famine; and she shall be utterly burned with fire: for strong is the Lord God who judgeth her.

  18 And cried when they saw the smoke of her burning, saying, What city is like unto this great city!

Or is it referring to the day of the second advent?

II Thessalonians 1:7 And to you who are troubled rest with us, when the Lord Jesus shall be revealed from heaven with his mighty angels,

  8 In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ:

Or is it referring to the end of the thousand year kingdom?

Revelation 20:9 And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them.

II Peter 3:7 But the heavens and the earth, which are now, by the same word are kept in store, reserved unto fire against the day of judgment and perdition of ungodly men.

  10 But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up.

  12 Looking for and hasting unto the coming of the day of God, wherein the heavens being on fire shall be dissolved, and the elements shall melt with fervent heat?

Or is it somehow referring to all of them?