As the sun's enlivening eye. J. Newton. [Parting.] Bull, in his life of Newton, p. 222, gives the following account of the origin of this hymn:—
"In November  Mr. Newton underwent an operation for a tumour in his thigh. He was mercifully brought through it, and was very soon able to resume his ordinary duties. On this occasion he composed the 71st hymn, Bk. ii. in the Olney Hymns."
As intimated, the hymn appeared in the Olney Hymns, 1779, in 7 stanzas of 4 lines, and headed "Parting." It came into use in the older collections, and is still found in a few hymnals both in Great Britain and America. The hymn, "For a season called to part," which is given in the New Congregational Hymn Book, 1859, No. 848, and other collections, especially in America, is composed of stanzas iv., v., and vi. of this hymn.
-- John Julian, Dictionary of Hymnology (1907)