1.  Robert K. Headley, Jr..  c2003.  Married Well and Often: Marriages of the Northern Neck of Virginia, 1649-1800: Marriages and Marriage references for the Counties of Lancaster, Northumberland, Old Rappahannock, Richmond, and Westmoreland.  Genealogical Publ. Co., Baltimore, MD (online at Ancestry.com):

p. 321

SLAUGHTER, William & HODGKINS, Phebe (or HODGKIN) (wid.); bet. 7 May 1673 - 1 Sep 1675; bride was a dau. of Col. Toby (d. RapC 1658) & Phebe SMITH and the wid. of Wm HODGKINS (or HODGKIN) (d. RapC 1673); she may have mar. (3) Wm. PEACHEY; (RapC DW 1665-77;134; DW 1677-82:130; RB 1671-76:297; RC Misc. Recs. 1699-1724:19; Eaton:49; Slaughter:307)

This is a late first marriage for William.  Did he have a prior wife?

2.  George Norbury MacKenzie.  1907-12.  Colonial Families of the United States of America.  7 vols.  Vol. I by Grafton Press, New York; Vols. II-VII by Seaforth Press, Baltimore, MD (republ. 1966/95 by Genealogical Publ. Co., Baltimore, MD; Broderbund CD-189; online at Ancestry.com).

v.5 p. 460

Slaughter JOHN SLAUGHTER, the immigrant ancestor, settled in Virginia prior to 1620.  His three sons were     I.   FRANCIS, of whom later.   II.   William, High Sheriff of Essex County, Virginia, 1685; m. Phoebe, dau. of Col. Toby SMITH.   III.   Richard.

3.  Mary Denham Ackerly & Lula Eastman Jeter Parker.  c1930.  Our Kin:  the Genealogies of Some of the Early Families Who Made Histor in the Founding and Development of Bedford County, Virginia.  J.P. Bell, Lynchburg, VA (online at Ancestry.com):  this is the most fact-filled genealogy — need to extract.

4.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).