Musannaf Ibn Abi Shayba 17:1279

'Ali ibn Mushir narrated to us, from Abu Hayyan, from his father, who said: 'Abdullah ibn 'Amr and Ibn 'Umar met and spoke privately to one another. Then, each of them departed to his companions. Ibn 'Umar departed while he was weeping. It was said to him, "What makes you weep?" He said, "That which this one claimed he heard the Messenger of Allah (ﷺ) say has made me weep: 'No one shall enter Paradise who has in his heart the weight of a mustard seed of pride.'"