1 Kings 1:3

So the Philistines gathered together and came and camped in Shunem; and Saul gathered all Israel together, and they camped in Gilboa.

Then he said, “Please speak to Solomon the king, for he will not turn you away, that he may give me Abishag the Shunammite as a wife.”

So she said, “Let Abishag the Shunammite be given to Adonijah your brother as a wife.”

Now David became old and full of days, and he made his son Solomon king over Israel.

Furthermore, if two lie down together they keep warm, but how can one be warm alone?