Rashi on Exodus 35:5/רש"י על שמות ל״ה:ה׳

1נדיב לבו [WHOSOEVER] IS OF A WILLING HEART — Because his heart prompts one to generosity, he is called נדיב לב, one who is prompted to generosity by the heart. I have already explained the various materials which formed the contribution towards the Tabernacle and the work done for it in the passages where the commands about them were given.