464. Amīr al-mu’minīn, peace be upon him, said: The Banū Umayyah (Umayyids) have a fixed period (mirwad) wherein they are having their way. But when differences arise among them then even if the hyena attacks them it will overpower them.
قال السيد الرضي: وَالْمِرْوَدُ هاهنا مفعَل من الإرْوَاد، وهو الإمهال وَالإظهار، وهذا من أفصح الكلام وأغربه، فكأنه (عليه السلام) شبّه المهلة التي هم فيها بالمضمار الذى يجرون فيه إلى الغاية، فإذا بلغوا مُنقَطَعها انتقضَ نظامُهم بعدها.
as-Sayyid ar-Raḍī says: Herein “mirward” is a form derived from “irwād” which means to allow time, to wait for. It is an extremely eloquent and wonderful expression. It is as though Amīr al-mu’minīn, peace be upon him, has likened the period of Banū Umayyah to a limited area meant for the training of horses for racing where they are running towards the limit, so that when they reach its extremity their organization will be destroyed. 
 This is the prophecy about the decline and fall of the Umayyads that proved true, word for word. This rule was founded by Mu‘āwiyah ibn Abī Sufyān and ended with Marwān ibn Muḥammad al-Ḥimār in 132 A.H. after a life of ninety years, eleven months and thirteen days. The Umayyads period was second to none in tyranny, oppression, harshness and despotism. The despotic rulers of this period perpetrated such tyranny that it put blots on Islam, blackened the pages of history and injured the spirit of humanity. They allowed every kind of ruin and destruction only to retain their own personal authority. They led armies to Mecca, hurled fire on the Ka‘bah, made Medina the victim of their brute passions, and shed streams of Muslim blood. At last, this bloodshed and ruthlessness resulted in revolts and conspiracies from all sides and their internal strife and agitation and their mutual fighting paved the way for their ruin. Although political unrest had set in among them earlier yet during the days of al-Walīd ibn Yazīd open disturbances began to occur. On the other side Banū al-‘Abbās (the ‘Abbāsids) also started preparations and during the reign of Marwān al-Ḥimār they started a movement under the name of “al-khilāfah al-Ilāhiyyah” (the Caliphate of Allāh). For successful piloting of this movement they got a martial leader Abū Muslim al-Khurāsānī who, in addition to his knowledge of political events and occurrences, was also an expert in the art of warfare. Making Khurāsān as the base he spread a whole net against the Umayyads and succeeded in bringing the ‘Abbāsids to power.
In the beginning this man was quite unknown and it is for this unknowness and low position that Amīr al-mu’minīn likened him and his associates to the hyena as this simile is used for low and humble people.