Tan Boon Wah v. Datuk Seri Ahmad Said Hamdan, Ketua Suruhanjaya, Suruhanjaya Pencegahan Rasuah Malaysia and Others was a case decided in the High Court at Kuala Lumpur in Malaysia in 2009. The High Court for the first time defined the meaning of the phrase "day to day" in law, applying it specifically to the Malaysian Anti-Corruption Commission Act. Ruling that "day to day" refers to general office hours, the High Court held that it was illegal to interrogate suspects or prisoners during the night time, and that doing so violated Article 5 of the Constitution, which protects personal liberty.