Candles and bibles in hands, people marched in defiance of a ban on demos against President Joseph Kabila.
After Sunday Mass, Christians took to the streets of Kinshasa, the capital of the Democratic Republic of Congo, demanding an end to Kabila's 17-year rule.
Six people were killed as security forces cracked down on protests, and at least 33 people were wounded across the country.
"I am a convinced Muslim and I am telling the Muslim community that because we share common values with our fellow Christians and most of all we are all Congolese, we have a duty to eradicate evil," said Siradji Nyalamba from the Union for Democracy and Social Progress party.
"That is why I came to join the Catholic organization to defeat this government that has failed," he added.
In power since 2001, Kabila's mandate ended in December 2016. Under a deal brokered by the Catholic Church he was allowed to remain in office provided new elections were held in 2017, but a new ballot is not scheduled until December 2018.