A man attacked his elderly mother after she refused to disclose the personal identification number (PIN) of her ATM card.

He also threatened to cut the 77-year-old's fingers with a knife.

Badly injured, she crawled out of bed the next day.

Adrian Yap Yin Leung, 56, was sentenced to jail for five years and three months yesterday.

He pleaded guilty to one count each of voluntarily causing hurt to his mother while robbing her and subsequently failing to report to the police for investigations.

One other charge of possessing a false Singapore passport was taken into consideration during sentencing by District Judge Ronald Gwee.

On Oct 16, 2018, at about 11pm, Yap and his mother, Madam Eunice Tsang Siew Geok, were in the unit she was residing in.

Court documents do not state if they were living together.

Wanting to withdraw money from his mother's POSB account for his own use, Yap asked her for the PIN of her ATM card.

When she refused to tell him, Yap hit her multiple times with her walking stick. He also kicked and stamped on her body, pulled her hair and threatened to cut all of her fingers with a knife.

Deputy Public Prosecutor Lim Woon Yee said that the assault stopped only after Madam Tsang relented and revealed her PIN.

"As she was badly injured and in great pain, the victim was unable to call for police assistance after the assault. She then lay down in her room to rest," said the DPP.

Yap left the unit at about 3am the next day and withdrew $2,000 from his mother's bank account.

Madam Tsang later sought assistance from her neighbours, who called the police after noticing the injuries on her face.

She was taken to Tan Tock Seng Hospital, where she was found to have injuries such as rib fractures.

DPP Lim said the woman became fearful of going out alone after the incident, for fear of being beaten up. She also had recurrent thoughts of Yap's assault.

He was arrested on Oct 26, 2018, and released on a personal bond the next day.

As a condition of the bond, he was required to report to Tanglin Police Station on Nov 9 that year, but failed to do so. He was arrested again on Aug 5, 2019.

Urging the court to sentence Yap to five years and three months' jail, DPP Lim noted how Yap had assaulted his mother who was "frail, helpless and unable to retaliate".

Yap's lawyer Ng Shi Yang said in mitigation that there was no premeditation to his client's assault.

District Judge Gwee backdated Yap's sentence to Oct 31, 2019, when he was first remanded.

When The Straits Times went to the unit yesterday, neighbours said the elderly victim had moved out about a year ago.

A domestic worker, who did not want to be identified, said she was the first person to see Madam Tsang early in the morning after the assault.

"She asked for help, and I was scared, so I quickly called my employer, who called the police," the maid said, adding that Madam Tsang lived with her elderly husband who was hearing-impaired, and they both required walking aids.

Another neighbour, who looked to be in her 60s and did not want to be identified, said the elderly couple moved out with a woman believed to be their daughter.

She added that they mostly kept to themselves and the unit has since remained vacant.