Ibn Jurayj (may Allah have mercy on him) said: More than one person told me that Sayyidah Fatimah (may Allah be pleased with her) was the youngest of the daughters of the Messenger of Allah (peace and blessings be upon him) and the most beloved of them to him (peace and blessings be upon him). And al-Zubayr bin Bakkar held that Sayyidah Ruqayyah (may Allah be pleased with her) was younger than Sayyidah Fatimah (may Allah be pleased with her).
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19189