Al-Qasim bin Ghannam narrates from his grandmother al-Dunya, from her grandmother Umm Farwah (may Allah be pleased with her), who was among those who gave the pledge of allegiance to the Prophet (peace and blessings be upon him) and was among the first women emigrants, that she heard the Prophet (peace and blessings be upon him) when he (peace and blessings be upon him) was asked about the best of deeds, and he (peace and blessings be upon him) said: "Offering the prayer at the beginning of its time."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2042