MIDRASH TEHILLIM
1.....(4.9)
Tremble and sin no more...
David said to the children of Israel, How long will you sin and stir up trouble by saying, There is a blemish in David, he is a descendant of Ruth the Moabite. Commune with your own heart upon your bed. From what sort of marriage bed do you come? From the prohibited marriage of a man to two sisters. Regard your own descent, and be still forever.
2.....(4.9)
pledge [this] in your hearts, upon your bed...
...God declared to Israel, I say to you, when you would pray,
go to the synagogue in your city,
when you cannot go to the synagogue in your city,
pray in your open field,
when you cannot go to your open field,
pray in your house,
when you cannot go to your house,
pray upon your bed,
when you cannot pray aloud in your bed,
commune with your heart.