When to stand for prayer

It is narrated from Sayyiduna Abdullah bin Abi Awfa (may Allah be pleased with him) that he said: "When Sayyiduna Bilal (may Allah be pleased with him) said (during the iqamah) the words 'Qad qamat al-salah' (The prayer has certainly been established), the Messenger of Allah (peace and blessings be upon him) would rise (to lead the prayer)."
Imam Abu Ya'la recorded this hadith in his Musnad. This narration explains the practice of the Prophet (peace and blessings be upon him) of standing up at the specific words of the iqamah.

It is narrated from Yunus bin Ubayd (may Allah have mercy on him) that "Imam Hasan al-Basri (may Allah have mercy on him) disliked that the takbir (to begin the prayer) be said before the muezzin had completed and finished his iqamah."
Imam Ibn Abi Shaybah recorded this report in al-Musannaf (no. 4461), and its chain is jayyid (good). It explains the juristic point that the sunnah time for the opening takbir is after the completion of the iqamah.