Written and first recorded by Paul Williams (1971).
Hit version by Three Dog Night (US #4/MOR #1/CAN #2 1971).
From the wiki: “‘An Old Fashioned Love Song’ was written by the noted songwriter Paul Williams, who originally intended the song for The Carpenters, and it was first recorded by Williams for his album Just an Old Fashioned Love Song. Although this was the first song Williams had written specifically for the Carpenters, Richard Carpenter rejected it, and so Williams offered the song to Three Dog Night. The Carpenters never recorded the song, but did perform it live on television with Carol Burnett a few months later.”
Three Dog Night, “An Old Fashioned Love Song” (1971):
http://youtu.be/BkkgYjazSkk
The Carpenters, “An Old Fashioned Love Song” TV performance (1971):