"The Toro and the Cavallino are together again... what a stable! Scuderia Toro Rosso's 2016 challenger, the STR11, will feature a Ferrari power unit," the Red Bull-owned team said on their website.
Ferrari supplied Toro Rosso from 2007 to 2013. Current Ferrari driver Sebastian Vettel took his first F1 win with the team in 2008.
"Because of the last minute nature of the decision relating to our power unit supply for next year, the team will use the very last specification used in the 2015 season," Toro Rosso added.
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Ferrari finished the season as overall runners-up, with their engine more reliable and offering better performance than the Renault unit used by Toro Rosso.
"With our engine supplier just a short drive up the autostrada and even linguistically, the return to Ferrari will make for an easy working relationship," Toro Rosso said.
"Taking this into account, and considering the past achievements with our friends from Maranello, we can certainly expect an improvement in our performance next year.
"We can also count on Carlos and Max who, after being confirmed for the 2016 season, will be able to translate all this year's learnings and experience into additional valuable feedback throughout the season."
Dutch driver Verstappen, who turned 18 during the season, was the highest-placed rookie of the year with a best result of fourth. Spaniard Sainz, son and namesake of the former world rally champion, also impressed and outqualified his team mate over the course of the season.
Renault announced on Thursday that they would return as a full works team next year after taking over Lotus.
Red Bull will be using an engine provided by Renault but with the branding of the team's new partner, luxury watchmaker Tag Heuer.
(Reporting by Alan Baldwin, editing by Martyn Herman)
