"Pericles, Prince of Tyre" (in part) by William Shakespeare, 1619:

Sit down: thou art no flatterer:
I thank thee for it; and heaven forbid
That kings should let their ears hear their faults hid!

"The Works of Mr de St. Evremont," by Saint-Evremond, 1700:

... Heaven forbid that I should ever be so wickedly given as to dissuade your Grace....

"Hudibras," by Samuel Butler, 1709:

…And if she should, which Heaven forbid,
O'erthrow me, as the Fidler did;….

"King Henry IV" by William Shakespeare, 1559:

Edw. Lord Warwick, on thy Shoulder will I lean,
And when thou fail'st (as God forbid the Hour)
Must Edward fall, which peril Heaven forfend.

"K. Edward IV. and Tanner of Tamworth," in "Reliques of Ancient English Poetry" by Thomas Percy, 1767:

Marrye heaven forfend, the tanner replyde,
That thou my prentise were:
Thou wouldst spend more good than I should winne
By fortye shilling a yere.

"The London Review," 1767:

…—So says Mr. Heely, and heaven forfend that discord should reach his ear from our commendations!...

...all found with Google Book Search.