Musnad Ahmad 1153:1038

Waki' narrated to us, Isma'il bin 'Abd al-Malik narrated to us, from Ibn Abi Mulaykah, from 'Aishah, who said: The Prophet, may Allah bless him and grant him peace, went out from my presence while he was comforted in eye and pleasant of soul. Then he returned to me while he was sad. I said: "O Messenger of Allah, you went out from my presence while you were comforted in eye and pleasant of soul, and you returned while you were sad?" He said: "I entered the Ka'bah, and I wished that I had not done so. I fear that I may have burdened my nation after me."