He went to the mosque to break his fast with a sweetened drink but got a mouthful of soap instead.
The incident happened at the Muhajirin Mosque on Tuesday.
Like many mosques in Singapore during the holy month of Ramadan, the mosque at Braddell Road provides food for Muslims to break their fast at dusk.
Mr Muhammad Zuhal Abdul Lathif, a religious teacher, had taken his son, 7, to break fast at the mosque.
The feast was held in the mosque's common space just outside the main prayer hall.
Unfortunately, Mr Muhammad Zuhal's break fast took an unpleasant turn when his son took a sip of a chilled pink syrup drink. The little boy recoiled in shock.
"He shouted at me, 'What is this dad!?'" said Mr Muhammad Zuhal, 43.
"I took a small sip of the drink to test it and find out why my son was shouting. It was really bitter and it tasted like soap."
His son then vomited. Fortunately, that was the only time he did so, Mr Muhammad Zuhal said.
"He was able to go to school yesterday so he is okay now. But after he vomited, he looked really pale."
Mr Muhammad Zuhal then told the people around him not to drink the liquid.
"When I was in the toilet with my son to rinse my mouth, I heard an announcement made by the mosque officials informing everyone to not drink the liquid," he said.
A mosque spokesman confirmed the incident yesterday.
"On Tuesday, while preparing drinks for the breaking of fast, a volunteer mistakenly poured some liquid soap into the container meant for the drinks, thinking that it was strawberry syrup," he said.
The mosque said the volunteer has been with them for more than five years and this was the first time that such an incident occurred.
"We are truly sorry about the incident and that Mr Muhammad Zuhal and his son had to go through something so unpleasant," the spokesman said.
"We take full responsibility and we will reimburse anyone who had to visit the doctor because of this incident."
The spokesman said that although there were more than 100 people who broke their fast at the mosque on Tuesday night, their investigation showed that there were fewer than 10 people who consumed the drink.
Islamic Religious Council of Singapore (Muis) released a statement about the incident on Wednesday, expressing regret that such an incident happened.
"This was an isolated incident and the volunteer has been counselled by the mosque," a Muis spokesman told The New Paper on Wednesday.
"The mosque chairman would apologise to the congregation at today's iftar (breaking of fast) and seek their continued support and trust."
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