One of the many passages in the New Testament where Paul talks about this theme is 2 Corinthians 11, and I have included a link below to a site which gives a more in depth discussion of this chapter. However, note that in this chapter Paul talks rather dismissively of Paul apostles and distinguishes himself from them in a number of different ways. Note how he describes them in verses 13-15 and the harsh words that he uses:

For such men are false apostles, deceitful workmen, masquerading as apostles of Christ. And now, for Satan himself masquerades as an angel of light. It is not surprising, then, if his servants masquerade as servants of righteousness. Their end will be what their actions deserve.

In contrast to these harsh words, Paul argues that he is different from them in a number of key ways. In fact this whole chapter is included in this book to prove Paul's legitimate status as a true apostle. He refused payment for his services, unlike others. For him it was always a principle to never be a burden on anyone, as it says in verses 7-12. In addition, Paul goes on for some length about the various sufferings he has endured to preach the Gospel, sufferings that are severe and serious but also show that he cannot be a false apostle, for what apostle would endure such hardships if they were false? Lastly, Paul boasts, but boasts in his weakness, as it says in verse 30. He does this again to add veracity to his claims of being a true apostle.