Awwam bin Hamzah says: I asked Abu Uthman (may Allah have mercy on him) about qunut in the morning prayer, and he said: It is after the ruku'. I asked: From whom did you take this? He said: From Abu Bakr, Umar and Uthman (may Allah be pleased with them).
This chain is hasan (good), and Yahya bin Sa'id narrates only from those who are trustworthy in his view.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3108