Musnad Ahmad 1017:113

Yahya ibn Sa'id narrated to us, from Hisham and Isma'il. Hisham informed us, Yahya ibn Abi Kathir narrated to us, from Abu Qilabah, from Abu al-Malih, who said: We were with Buraydah on a military expedition on a cloudy day. He said: "Perform the prayer early, for the Messenger of Allah (peace and blessings of Allah be upon him) said: 'Whoever leaves the Asr prayer, his deeds are rendered void.'"