Musannaf Ibn Abi Shayba 3:127

'Abdah ibn Sulayman narrated to us, from Mis'ar, from Yazid al-Faqir, who said: Ibn 'Umar used to omit the takbir in prayer. Mis'ar said: When he would descend after the bowing (ruku') and not say the takbir, then when he intended to prostrate for the second (prostration), he would not say the takbir.