It depends on the country's entry requirement you are visiting.
Trust me, my sis went into a frenzy when she realised her passport left 3 months validity when she was doing last minute packing for her HK holiday the next day. It was Saturday afternoon when she realised too, so ICA building is closed. Flight was on Sunday, and she was panicking. After many calls to and fro SIA hotline (their Pinoy CSOs are useless, btw), and calling the ICA officer in Changi Airport, I told my sis to just go down to the airport there and then to ask them face to face.
So she did, and the boarding officer checked their system for her and said HK needed only one month validity, so she will be cleared upon check-in, no worries.
And so she made the trip, enjoyed the holiday, and came back - with no hiccups, despite having only 3 mths of validity left in her passport.
Of course, one should always try to renew before your passport hit that 6 mths validity, since a lot of countries have that entry requirement. My sis was lucky - HK wasn't one of them.
However, TS is going Malaysia... and
unfortunately, Malaysia is like Singapore - you need at least 6 mths validity.
Entry Requirements to Malaysia : Malaysia LCCT, Relevant Malaysia Travel Info For Your Journey