And I heard Ishaq — another time — say: "If he catches the Imam while bowing, the Sunnah in that is to say one Takbir with which he opens the prayer while standing. He should not begin descending during the opening Takbir; for if he does not complete the opening Takbir while standing, it will never suffice him. Once he has said the opening Takbir, he descends to bow after the Takbir for bowing. If the Takbir for bowing occupies him such that the Imam is about to rise, and he does not fear, he should say the Takbir for bowing while descending. He should not say 'Subhanaka Allahumma...' nor the seeking of refuge, nor anything with which he opens the prayer if he fears that the Imam will raise his head before he descends for bowing and places his hands on his knees. If it is possible for him to remain in his bowing for the duration of what he says after the opening Takbir, 'Subhanaka Allahumma...' or something he says to open the prayer with, for the duration of his bowing before the Imam raises his head—or not, before he descends for bowing he placed his hands on his knees, and he does not count that rak'ah, and also if he doubts whether he caught it with the Imam before he raised his head."

767 - Ishaq narrated to us, he said: Zakariyya ibn 'Adi informed us, from 'Ubayd Allah ibn 'Amr al-Ruqi, from Ishaq ibn Rashid al-Jazari, from al-Zuhri, from Salim, from his father, who said: "If he says the Takbir to bow, then descends for bowing, and the Imam raises his head, and he is uncertain as to whether he bowed before the Imam raised his head or not, he does not count that rak'ah."