Paul said the day of the Lord comes as a thief in the night

1Th 5:1-11 But of the times and the seasons, brethren, ye have no need that I write unto you. For yourselves know perfectly that the day of the Lord so cometh as a thief in the night. For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape. But ye, brethren, are not in darkness, that that day should overtake you as a thief. Ye are all the children of light, and the children of the day: we are not of the night, nor of darkness. Therefore let us not sleep, as do others; but let us watch and be sober. For they that sleep sleep in the night; and they that be drunken are drunken in the night. But let us, who are of the day, be sober, putting on the breastplate of faith and love; and for an helmet, the hope of salvation. For God hath not appointed us to wrath, but to obtain salvation by our Lord Jesus Christ, Who died for us, that, whether we wake or sleep, we should live together with him. Wherefore comfort yourselves together, and edify one another, even as also ye do. 

Peter said the day of the Lord comes as a thief in the night in which the heavens pass away

2Pe 3:10 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. Seeing then that all these things shall be dissolved, what manner of persons ought ye to be in all holy conversation and godliness, 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? Nevertheless we, according to his promise, look for new heavens and a new earth, wherein dwelleth righteousness. Wherefore, beloved, seeing that ye look for such things, be diligent that ye may be found of him in peace, without spot, and blameless.  

Both Paul & Peter said the Day of the Lord Comes as a Thief in the Night

Lets see what the Prophets from the Old Testament said the Day of the Lord is