Musannaf Ibn Abi Shayba 23:91

'Isa and Waki' narrated to us, from al-Awza'i, from Yahya ibn Abi Kathir, from Abu Qilabah, from Abu al-Muhajir, from Buraydah, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever leaves the 'Asr prayer, his deeds have become void."