NEW YORK (AP) _ A 1788 letter in which Benjamin Franklin denounced slavery as ``repugnant'' to the principles of the then-new American nation, and another written by ex-slave and abolitionist Frederick Douglass to his former owner were sold at auction Tuesday.

``I love you. But hate slavery,'' Douglass, then about 77, told B.F. Auld, the son of his former master in Baltimore, Md., in a 1894 letter asking for help in finding out the exact date of his birth. ``I have always been troubled by the thought of having no birthday,'' Douglass wrote.

The Franklin letter was sold to an anonymous telephone bidder for $305,000, including Sotheby's commission, close to the pre-sale estimate.

In spirited bidding, the Douglass letter was acquired for $46,000 by a buyer for the Gildor-Lehrman Collection, an historical document archive at New York's Pierpont Morgan Library.

An 1865 copy of the Thirteenth Amendment outlawing slavery, valued at $60,000 to $80,000 presale, went for $68,000.

Douglass, born into slavery around 1817, was educated by the Auld family, but banished to the fields after the death of the senior Auld, his chief benefactor. In 1838 he escaped, fled north and became a crusading leader of the anti-slavery movement.

In his letter to then-Gov. Samuel Huntington of Connecticut, Franklin said the Pennsylvania Society for Promoting the Abolition of Slavery, which he then headed, had learned many slaves were being imported in ships built in the United States.

Franklin asked Huntington to use his influence to ``prevent a practice which is so evidently repugnant to the political principles & forms of government lately adopted by the Citizens of the United States.''