He told me, he was just in the same situation [i. e. in a garden], as when formerly, the notion of gravitation came into his mind. It was occasion'd by the fall of an apple, as he sat in a contemplative mood. Why should that apple always descend perpendicularly to the ground, thought he to him self. Why should it not go sideways or upwards, but constantly to the earths centre? Assuredly, the reason is, that the earth draws it. There must be a drawing power in matter.

A Hastings White (ed.) Memoirs of Sir Isaac Newton's Life (1936) pp. 19-20. (1752)