“Also about the Conclusion of the Psalmes [Psalter], we had no debate with them; without scruple, Independents and all sang it [the doxology], so far as I know, where it was printed at the end of two or three psalms. But in the new translation of the Psalmes [the eventual 1650 Psalter], resolving to keep punctually to the original text, without any addition, we and they were content to omit that [doxology] whereupon we saw both the Popish and Prelatical parties did so much dote, as to put it to the end of the most of their lessons, and all their psalms.” Robert Baille, April 25, 1645, Letters of Robert Baillie, Vol II, p 259.
Robert Baillie stated this after the Westminster Assembly decided to remove an uninspired Doxology from what would become the authorized 1650 Psalter. Baillie admits that most men sang it without any scruple, but then he makes it clear why they eventually removed it from the Psalter…it was not an inspired part of the original text.
This was the doxology in question:
To Father, Son and Holy Ghost
The God whom we adore
Be glory as it was, is now
And shall be evermore.
David Silversides uses this quote by Baillie to make the following point:
“Later Scottish Covenanters, like Brown of Wamphray and McWard (contending with Bishop Burnett) opposed the sung doxology, not because they deemed its content doctrinally unsound, but because of the regulative principle of worship and the absence of Scriptural warrant to add anything to the 150 Psalms given by God. From the deliberate exclusion of the doxology we learn that the Westminster Confession means by the “singing of psalms” (in ch.xxi, para. v) simply the use of the Biblical Psalms.”
The paper by David Silversides is found here
Exclusive Psalmody 