Luke 8:31

‘And they entreated him that he would not command them to depart into the abyss.'

Jesus' persistence in seeking to cast them out was being effective, and now that He knew the detail of what possessed the man they knew that they could not hide themselves any longer. So they did the next best thing and pleaded that at least they might be spared ‘the Abyss' (abusson = ‘bottomless, boundless'). This was the name of the place where evil spirits were imprisoned until the final days (Revelation 9:1; Revelation 9:11; Revelation 11:7; Revelation 17:8; Revelation 20:1; Revelation 20:3; Compare 1 Peter 3:19; 2 Peter 2:4; Jude 1:6).

Jesus is said to have descended into the Abyss, mentioned in Romans 10:7, but there it simply referred to the boundless world of the departed. However, in Revelation the Abyss is that part of the world of the departed which is the prison of evil spirits (compare 2 Peter 2:4; Jude 1:6). ‘Abyss' is also related to Sumerian apsu, the sea. This is confirmed by the fact that the Septuagint (LXX) translated ‘the deep' (tehom) of Genesis 1:2; Genesis 7:11; Genesis 8:2 as the ‘Abyss', paralleling the two (compare also Job 38:16; Psalms 33:7; Psalms 42:7; Psalms 77:16; Isaiah 51:10; Ezekiel 26:19; Jonah 2:5). Ironically therefore it may be that we are to see that the final end of these particular evil spirits was the Abyss after all, for they were later swallowed up by the sea. But note that they did acknowledge Jesus' right to command what He wanted. They acknowledged it of men did not.