On Twitter, Morales said that parents, children and grandchildren were once the victims of the dictatorship in Argentina, and now their mothers and grandmothers are victims because they fight for justice.
The 90-year-old activist was ordered to appear in court to testify after her organization, Mothers of the Plaza de Mayo, was accused of siphoning off public funds from a social housing program known as "Shared Dreams."
The Mothers of the Plaza de Mayo was set up to search for missing children from the years of the dictatorship, but has long since expanded its mission in the fight for human and social rights.
“Our solidarity with the Mothers and Grandmothers of Plaza de Mayo, respect and admiration for the great defenders of life and freedom,” said Evo Morales.
Argentine Judge Marcelo Martinez de Giorgi issued the detention order against Bonafini Thursday after she failed to appear in court. The 90-year-old activist later explained her absence.
Remembering Latin America's Disappeared
"When judges are in power and are paid by those in power, (and) they force us mothers to testify, someone has to rebel, and us mothers really are rebels... we will not testify," she said.
Bonafini has previously expressed support for the Bolivian leader. "What is happening in Argentina is very sad and serious. I send a big hug to Evo, he's an amazing man, who has shown us how to build a country," she said back in 2015.
The Mothers hold a customary weekly march every Thursday since 1977, to commemorate the victims of the U.S.-backed Dirty War that disappeared some 30,000.