I think it’s on Hallel. Definitely not MBD.
I don’t know too much of it but here’s some.
My sefer tehillim,
I’ve always held you so dear,
You help me express my deepest thoughts,
You taught me not to fear.
Your words are engrained upon my heart,
Your pages have felt my tears,
You help me express me deepest thoughts (I think?)
……..(not sure what’s next)
Maybe if each poster adds another line, you’ll end up with the whole song.