Parshas Ekev
It says in the posuk ‘and all the diseases of Mitzrayim, I will not put upon you, and I will give them to your enemy’. When the posuk says ‘I will not put’, it uses the words ‘lo yesimum’ from the root ‘sim’, why when it speaks about putting them on your enemy it uses the words ‘Unesanam’ from the root ‘tein’.
Both words mean to give. Chazal explain that ‘tein’ means a big giving whereas ‘sim’ means any giving. We interpret the posuk to mean that Hashem will not give any sickness to the jews, whereas to their enemies he will give a big giving of disease. -Malbim