A scuffle broke the reflective atmosphere of Friday prayers in Riyadh's al-Ferdous mosque after the imam deplored the recent bloody crackdown on Muslim Brotherhood protesters by the military in nearby Egypt.
The fight between members of the congregation, recorded on a widely circulated Youtube clip and reported by the daily al-Hayat newspaper, demonstrated how high feelings are running in the devoutly Muslim kingdom.
While they have been careful to express only muted dissent in public, Islamists and some other conservative Gulf Muslims are quietly seething at Saudi Arabia's whole-hearted backing of Egyptian army chief General Abdul Fattah al-Sisi.
After Sisi's military seized power last month, a group of clerics in the kingdom signed a letter calling on King Abdullah to reverse his position, and since the violence began two weeks ago, many Saudis have spoken out on social media.
"For Riyadh to be in the frontline of a confrontation like what is taking place in Egypt is unprecedented. It is making ripples inside Saudi Arabia," said a Saudi journalist.
Saudi King Abdullah and the rulers of the United Arab Emirates, and to a lesser extent of Kuwait, have long distrusted the Muslim Brotherhood, which they feared would use its power in Egypt to agitate for political change across the Middle East.
When Sisi ousted Mohamed Mursi of the Brotherhood as president, the three monarchies promptly gave Egypt's secular new government $12 billion in aid. When, with much bloodshed, security forces moved to clear Brotherhood protest camps, they all spoke strongly in support.
Though Islamist anger is unlikely to erupt in a significant public way at the moment, or to change Gulf support for Sisi, analysts say, it is something the region's states are watching.
The al-Saud family has always regarded Islamist groups as the biggest threat to its rule over a country where appeals to religious sentiment can never be lightly dismissed and where Muslim militants have previously targeted the state.
Last decade it fought off an al Qaeda campaign of attacks targeting officials and foreigners that killed hundreds. In the 1990s, the Sahwa, or "awakening", movement inspired by the Muslim Brotherhood demanded political reforms that would have weakened the ruling family.
That history of Islamist opposition to the Saudi authorities was echoed on Sunday in a letter published by Sheikh Ibrahim al-Rubaish, the main ideologue of al Qaeda in the Arabian Peninsula, attempting to leverage public disquiet over Egypt.
"The Saudi position is generally in favour of Godlessness," he wrote.
BROTHERS IN ISLAM'S CRADLE
While al Qaeda is now thought by analysts to have very little public support in Saudi Arabia, more mainstream Islamist ideas are common.
Waleed Abu al-Khair was a Jeddah high-school student when a friend from his mosque phoned up late one night and asked him to come over to his house, alone.
"When I got there, he told me: 'I am a member of the Muslim Brotherhood and I want you to become one, too. It will be a secret between us'," said Abu al-Khair, now a prominent liberal and human rights activist.
That midnight conversation not only launched Abu al-Khair into a five-year association with the Brotherhood, but cast a light on its conspiratorial habits that are so alarming to the authorities.
During a later investigation into his work as a human rights activist, government officials told Abu al-Khair they had been aware of all his movements as a Brotherhood member, monitoring his "family" of six supposedly secret cell members.
It was a sign of how seriously the Saudi authorities view the threat posed by Islamists who want political change.
"They rose up against the kingdom," said the late interior minister Prince Nayef in 2002, expressing the sense of betrayal behind Saudi mistrust of the Brotherhood.
After Saudi Arabia gave shelter to Brotherhood members fleeing persecution in Egypt in the 1960s, some of them used their role in the kingdom's education system to help young Saudis to create the Sahwa movement.
Although the Sahwa was eventually crushed with firm policing, some of its leading clerics, such as Sheikh Salman al-Awdah, remain influential.
During the past week, Awdah's Twitter picture has featured the four-fingered salute on a yellow background that represents those who were killed in Cairo's al-Rabia Square a week ago, a tacit statement of opposition to the government line.
GULF JITTERS
Saudi distrust of the Brotherhood is felt even more keenly in the UAE, which this year said it would put on trial 30 suspected members accused of plotting a coup.
But on social media, the main forum used in Gulf monarchies to express views that run against the official line, many users claiming to be Emirati posted under a hashtag saying "the foreign ministry's statement (on Egypt) does not represent me".
In Kuwait, Brotherhood members are not only able to speak in public, but are respectable members of society, joining the country's parliamentary opposition last year despite the ruling al-Sabah family's private misgivings.
"We found surprising the speed with which the Kuwaiti government gave support to the military government which returned to power in Egypt undemocratically," Osama al-Shaheen, a former member of parliament for the Brotherhood's Kuwaiti wing, the Islamic Constitutional Movement, told Reuters.
Describing Kuwait's position as "naive", he added the Brotherhood was not alone in the country in opposing the Egyptian military's seizure of power.
"Many jurists and politicians were ahead of us. They are the leaders in condemning the coup," he said.
LIGHT GOVERNMENT HAND
Despite these rumblings, however, Gulf governments have used a relatively light hand to counter the dissent.
Sheikh Awdah's television show, on a privately owned channel, was recently cancelled. Two other prominent Islamists, Sheikh Mohammed al-Arefi and Mohsen al-Awaji, were summoned to meet the authorities after signing a petition against Mursi's removal, but they were not formally arrested.
Last week, billionaire Saudi Prince Alwaleed bin Talal, a media mogul, sacked a Kuwaiti cleric who had been preaching on one of the religious channels he owns, for his relationship with the Muslim Brotherhood.
In Kuwait, the government is planning to redraw its rules on what imams can say in mosque sermons to stop them talking about politics in other Arab countries, the liberal daily al-Qabas reported. It also deported nine Egyptians for protesting against the support for Sisi last week.
"The Saudi government decided not to arrest anyone. Their assessment is that the Islamists do not enjoy a lot of support," said Mustafa Alani, head of security studies at the Gulf Research Centre in Geneva.
But while Gulf governments are not using the security apparatus to make their argument, they are deploying both loyal media and senior, state-employed clerics.
Saudi newspapers have repeatedly splashed statements by King Abdullah and Foreign Minister Prince Saud al-Faisal dismissing Brotherhood protests in Egypt as terrorism and sedition.
The Grand Mufti's Friday sermon last week preached the need to avoid extremism and conflicts that cause "great calamity" to the ummah. His advice against "deviation" was pointed, given that Saudi Arabia refers to Islamist militants such as al Qaeda as "deviants".