Hazrat Zahra (peace be upon her) in her historical sermon said:
وَ طَاعَتَنَا نِظَاماً لِلْمِلَّةِ وَ إِمَامَتَنَا أَمَاناً لِلْفُرْقَة
“…our obedience is the system for religion and our Imamat is a security from disunity…”
References:
1. Balaaghaat al-Nisaa, p. 28
2. Al-Ehtejaaj, vol. 1, p. 99,
3. Behaar al-Anwaar, vol. 29, p. 223 and 241