Musannaf Ibn Abi Shayba 13:2077

Abu Bakr narrated to us, he said: Isma'il ibn 'Ayyash narrated to us, from 'Amr ibn Muhajir, that 'Umar ibn 'Abd al-'Aziz said: "Al-Najash (bidding up the price without the intention to buy) is not lawful."