It is narrated from Sayyidah Aishah (may Allah be pleased with her) that she said: "The Messenger of Allah (peace and blessings be upon him) would stand in these two rak'ahs (of the sunnah of Fajr) only for as long as it takes to recite Surah al-Fatihah."
The chain of this hadith is sahih (authentic). Imam Ibn Abi Shaybah narrated it in his book al-Musannaf (hadith: 613), and all its narrators are thiqat (trustworthy).
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب النوافل / 613