8 On that day David had said, “Anyone who conquers the Jebusites will have to use the water shaft to reach those ‘lame and blind’ who are David’s enemies.a ” That is why they say, “The ‘blind and lame’ will not enter the palace.”

Read 2 Samuel 5:8 Using Other Translations

And David said on that day, Whosoever getteth up to the gutter, and smiteth the Jebusites, and the lame and the blind, that are hated of David's soul, he shall be chief and captain. Wherefore they said, The blind and the lame shall not come into the house.
And David said on that day, "Whoever would strike the Jebusites, let him get up the water shaft to attack 'the lame and the blind,' who are hated by David's soul." Therefore it is said, "The blind and the lame shall not come into the house."
On the day of the attack, David said to his troops, “I hate those ‘lame’ and ‘blind’ Jebusites. Whoever attacks them should strike by going into the city through the water tunnel. ” That is the origin of the saying, “The blind and the lame may not enter the house.”