Calon Lān (A Pure Heart) is a Welsh hymn, the words of which were written in the 1890s by Daniel James (1848-1920) and sung to a tune by John Hughes (1872-1914). The song has become associated with Welsh rugby union, being sung before almost every Test match involving the Welsh national team. It's also become a standard solo for many artistes. I was beaten into second place in the learner's solo at the Boduan Eisteddfod last year by a fine rendition of the song with piano accompaniment (much to my dismay, of course!). Here is the melody, in the key of G (which I can just about manage) rather than the original Bb (much too high for me!).
1. Nid wy'n gofyn bywyd moethus, I don't ask for a luxurious life, Aur y byd na'i berlau mān: The world's gold or its fine pearls: Gofyn wyf am galon hapus, I ask for a happy heart, Calon onest, calon lān. An honest heart, a pure heart. Calon lān yn llawn daioni A pure heart full of goodness Tecach yw na'r lili dlos: Is fairer than the pretty lily: Dim ond calon lān all ganu, None but a pure heart can sing, Canu'r dydd a chanu'r nos. Sing in the day and sing in the night. 2. Pe dymunwn olud bydol, If I would wish for worldly wealth, Chwim adenydd iddo sydd; It would fly have swift wings; Golud calon lān, rinweddol, The riches of a virtuous, pure heart Yn dwyn bythol elw fydd. Will bear eternal profit. 3. Hwyr a bore fy nymuniad Evening and morning, my wish Esgyn ar adenydd cān Soaring on the wing of song Ar i Dduw, er mwyn fy Ngheidwad, For God, for the sake of my Saviour, Roddi i mi galon lān. To give me a pure heart.
Some common alternatives now are as follows.
Here's the four-part setting of the song (from the Wikipedia page).