From Swiss Pictures Drawn with Pen and Pencil New Edition, Rev. S. Manning, Edward Whymper, illus., The Religious Tract Society, London, 1891.
A little more on Whymper here.
Climb if you will, but remember that courage and strength are nought without prudence, and that a momentary negligence may destroy the happiness of a lifetime. Do nothing in haste; look well to each step, and from the beginning think what may be the end.