From: Rabbi Moshe Sofer
To: Rabbi Yosef Yoel Deutsch
A rabbi asks whether sampling three handfuls of wheat to check for leavened grains validates an entire heap for Pesach. The Chasam Sofer rules strictly that finding leavened grains invalidates the heap since they originate from within it.
Source: Shu"t Chasam Sofer OC §136