Asher is the son of Andrew and Pegg, who had several children that were baptized at the First Church of Wells: Moab (1741), Nelle (1741), Andrew (1743), Asher (1747) and Nelle (1750).
Pegg was enslaved by John and Mary Wheelwright, and it is presumed that her children were as well. It is not known whether the father Andrew was also enslaved by the Wheelwrights.
In his will, Col. John Wheelwright left "all negro or molatto servants" to his wife Mary. He died in 1745.
In her 1750 will, Mary stated "my Negro Servant Woman named Pegg shall be divided to Such of my aforesd Daughters or grand Daughters which she shall choose to live with after my Decease" and "I will & give unto my beloved Daughter Sarah Jefferds a Negro Boy named Asher." Probate was recorded in 1755.
The aforesaid daughters and granddaughters were "Daughters Mary Moody & Sarah Jefferds, and my three beloved Grand Daughters, the Daughters of my dear deceased Daughter Hannah Plaisted, and my four beloved Grand Daughters the Daughters of my dear deceased Daughter Elizabeth Newmarch."
Sarah Jefferds' 1762 probate record abstract notes "a Negro boy at £40." Her 1763 probate abstract notes - "Acct includes Negro boy named Ashur appraised in inventory (£40) but conveyed to Capt. Simon Jefferds by a deed of the intestate (Sarah Jefferds' estate discharged from the Negro Ashur)." Capt. Simon may have likely been the son of Sarah and the Rev. Samuel, but this is not confirmed. Note that there was also a Capt. Samuel Jefferds who built and founded Jefferds Tavern in 1754 (per Shelley, p. 75); it's not clear whether he was a relation of either the Rev. Samuel Jefferds or of Capt. Simon Jefferds.
Bibliography:
Records of the First Church of Wells, as transcribed in 6 issues of the New England Historical and Genealogical Register, Vol 75-76, 1921-22