Musnad Ahmad 30:1650

Husayn narrated to us, he said: Sufyan—meaning Ibn ‘Uyaynah—narrated to us, from Abu al-Zinad, from ‘Abd al-Rahman al-A‘raj, from Abu Hurayrah, in a narration, that the Prophet (peace and blessings of Allah be upon him) said: "Do you see my Qiblah here? Nothing of your khushu‘ (humility/devotion) or your ruku‘ (bowing) is hidden from me."