"Al-'Imam Muhammad Al-Taqi (A), Al-'Imam 'Ali Al-Naqi (A), and Al-'Imam Al-Hasan Al-'Askari (A) were martyred when they were twenty

"Al-'Imam Muhammad Al-Taqi (A), Al-'Imam 'Ali Al-Naqi (A), and Al-'Imam Al-Hasan Al-'Askari (A) were martyred when they were twenty-five, forty, and twenty-seven years, respectively. All these points serve as a clear evidence that the control, surveillance, and sabotage of the antagonists was very strict during their period and that these great Imams (A) were unable to perform their duties freely. Nevertheless, valuable ahadith have reached us from these three great Imams (A) on the Usul al-Din (the fundamental principles of Islam for believing in) and the Furu' al-Din (the secondary principles of Islam for actions)."

ALLAMA TABATABAI (R)