Hard and fast ( বাঁধা ধরা ) There is no such hard and fast rule in this matter.
slap on the wrist ( মৃদু শাস্তি ) Although he broke the rules, he was only given a slap on the wrist
when pigs fly ( কখনও না ) I will help you when pigs fly
All at once ( হঠাৎ ) All at once a tiger came out of the forest.
To the contrary ( কাহারও বক্তব্যের বিপক্ষে ) In the court he said nothing to the contrary.
A blessing in disguise ( বিপরীতে হিত ; প্রথমে খারাপ হিসেবে মনে হলেও পরবর্তীতে ভালো হয় ) Sam's motorcycle accident was a blessing in disguise because he got enough insurance money.