He said Ramadan was a blessed month and Muslims should strive to improve themselves and stop quarrelling among themselves.
"Cut down on work that does not yield benefits and stop vilifying others.
"So, if we can all make use of Ramadan to increase worship without evoking things that invite dispute, surely we will be able to enjoy the beauty of Ramadan fully,” he said in an audio clip uploaded onto his Twitter account.
Referring to the by-elections in Kuala Kangsar and Sungai Besar last week, Najib said that despite the intense competition among the contesting political parties, the by-elections were over and done with.
As such, he said, all quarters should seek forgiveness, set aside differences and step up good practices during Ramadan, Bernama reported.
The Prime Minister also invited Muslims to engage in the Ramadan prayers with family and friends.