Abd al-Rahman ibn Muhammad ibn al-Ash'ath (died 704), commonly known as Ibn al-Ash'ath after his grandfather, was a prominent Arab nobleman and military commander during the Umayyad Caliphate, most notable for leading a failed rebellion against the Umayyad viceroy of the east, al-Hajjaj ibn Yusuf, in 700–703.

Ibn al-Ash'ath was a scion of a noble family of the Kinda tribe that had settled in the Arab garrison town of Kufa in Iraq. He played a minor role in the Second Fitna (680–692) and then served as governor of Rayy. After the appointment of al-Hajjaj as governor of Iraq and the eastern provinces of the Caliphate in 694, relations between al-Hajjaj and the Iraqi tribal nobility quickly became strained, as the policies of the Syria-based Umayyad regime aimed to reduce the Iraqis' privileges and status. Nevertheless, in 699, al-Hajjaj appointed Ibn al-Ash'ath as commander of a huge Iraqi army, the so-called "Peacock Army", to subdue the troublesome principality of Zabulistan, whose ruler, the Zunbil, vigorously resisted Arab expansion. In 700, al-Hajjaj's overbearing behaviour caused Ibn al-Ash'ath and the army to revolt. After patching up an agreement with the Zunbil, the army marched back to Iraq. On the way, the mutiny against al-Hajjaj developed into a full-fledged anti-Umayyad rebellion and acquired religious overtones.

Al-Hajjaj initially retreated before the rebels' superior numbers, but quickly defeated and drove them out of Basra. Nevertheless, the rebels seized Kufa, where supporters started flocking. The revolt gained widespread support among those who were discontented with the Umayyad regime, especially the religious zealots known as Qurra ('Quran readers'). Caliph Abd al-Malik tried to negotiate terms, including the dismissal of al-Hajjaj, but the hardliners among the rebel leadership pressured Ibn al-Ash'ath into rejecting the Caliph's terms. In the subsequent Battle of Dayr al-Jamajim, the rebel army was decisively defeated by al-Hajjaj's Syrian troops. Al-Hajjaj pursued the survivors, who under Ibn al-Ash'ath fled east. Most of the rebels were captured by the governor of Khurasan, while Ibn al-Ash'ath himself fled to Zabulistan. His fate is unclear, as some accounts hold that the Zunbil executed him after al-Hajjaj demanded his surrender, while most sources claim that he committed suicide to avoid being handed over to his enemies.

The suppression of Ibn al-Ash'ath's revolt signalled the end of the power of the tribal nobility of Iraq, which henceforth came under the direct control of the Umayyad regime's staunchly loyal Syrian troops. Later revolts, under Yazid ibn al-Muhallab in 720 and Zayd ibn Ali in 740, also failed, and it was not until the success of the Abbasid Revolution that the Syrian dominance of Iraq was broken.

Abd al-Rahman ibn Muhammad ibn al-Ash'ath was a member of a noble family from the Kinda tribe in the Hadramawt in eastern Yemen. His grandfather, Ma'dikarib ibn Qays, better known by his nickname al-Ash'ath (lit. 'He with the dishevelled hair'), was an important chieftain who submitted to Muhammad, but rebelled during the Ridda wars. Defeated, al-Ash'ath was nevertheless pardoned and married Caliph Abu Bakr's sister, Umm Farwa, who became his chief wife. He went on to participate in the crucial battles of the early Muslim conquests, Yarmouk and Qadisiyya, and held governorships in the newly conquered province of Adharbayjan. His role in the negotiations at the Battle of Siffin has led to his widespread condemnation in later, mainly pro-Shi'a sources, for persuading Ali to abandon his military advantage and submit to an arbitration that ultimately undermined his position. The real events remain unclear, but although al-Ash'ath was also close to Ali's Umayyad rivals—two of his daughters married into the Umayyad house—he nevertheless remained loyal to Ali, and another daughter married Ali's son al-Hasan. Al-Ash'ath later led the Kindite quarter in the garrison town of Kufa, where he died in 661.

Ibn al-Ash'ath's father, Muhammad (a son of Umm Farwa) was less distinguished, serving an unsuccessful tenure as Umayyad governor of Tabaristan, and becoming involved in the Second Fitna as a supporter of the anti-Umayyad rebel Ibn al-Zubayr, being killed in 686/7 in the campaign that overthrew the pro-Shi'a rebel leader Mukhtar al-Thaqafi. Like his father at Siffin, he is denigrated by pro-Shi'a sources for his ambiguous role in the Battle of Karbala in 680, being held responsible for the arrests of Muslim ibn Aqil and Hani ibn Urwa, prominent supporters of Ali's son, al-Husayn.

Ibn al-Ash'ath's mother, Umm Amr, was the daughter of the South Arab tribal leader Sa'id ibn Qays al-Hamdani. Ibn al-Ash'ath had four brothers, Ishaq, Qasim, Sabbah, and Isma'il, of whom the first three also fought in the campaigns in Tabaristan.

According to the 10th-century historian al-Tabari, the young Ibn al-Ash'ath accompanied his father and participated in his political activities: in 680 he helped arrest Muslim ibn Aqil. In 686/7, he fought under the Umayyad governor Mus'ab ibn al-Zubayr against Mukhtar, in the campaign in which his father was killed. After Mukhtar was killed during the fight, along with the other Kufan ashraf (Arab tribal nobility) who served under Mus'ab, Ibn al-Ash'ath urged the execution of Mukhtar's followers, who had barricaded themselves in the governor's palace in Kufa. This was not only to avenge the loss of their own kinsmen during the campaign, but also because of the deeply ingrained hostility of the ashraf to the non-Arab converts to Islam (the mawali), who had formed the bulk of Mukhtar's supporters. As a result, some 6,000 of Mukhtar's men were executed.