Sunan An-Nasai, Chapter: The Book of Leading the Prayer (Al-Imamah)

"A man from the Ansar came when the Iqamah for prayer had been said. He entered the Masjid and prayed behind Muadh, and he (Muadh) made the prayer lengthy. The man went away and prayed in a corner of the Masjid, then he left. When Muadh finished praying, it was said to him that so-and-so had done such and such. Muadh said: 'Tomorrow I will mention that to the Messenger of Allah (saw).' So Muadh came to the Messenger of Allah (saw) and told him about that. The Messenger of Allah (saw) sent for him and asked him: 'What made you do what you did?' He said: 'O Messenger of Allah, I had been working on my camel to bring water all day, and when I came the Iqamah for prayer had already been said, so I entered the Masjid and joined him in the prayer, then he recited such and such a Surah and made it lengthy, so I went away and prayed in a corner of the Masjid.' The Messenger of Allah (saw) said: 'Do you want to cause hardship to the people, O Muadh; do you want to cause hardship to the people, O Muadh; do you want to cause hardship to the people, O Muadh?'" (Sahih)