It is narrated from Hazrat Anas (may Allah be pleased with him) that all the prayers of the Prophet (peace and blessings be upon him) were nearly equal in length, and likewise the prayers of Hazrat Siddiq Akbar (may Allah be pleased with him). However, Hazrat Umar (may Allah be pleased with him) began to lengthen the Fajr prayer.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 13073