Both Sasuke and Madara's Sharingan awakened/evolved after they

The Mangekyou : r/Naruto

Rinnegan, The Gifted Half-Blooded Devil Uchiha Wiki

Strongest Uchiha in Naruto Ranked: Sasuke, Madara & More

Naruto: Why Sarada will likely get Mangekyo Sharingan

Is the Sharingan destined to die out? With sasuke and sarada only being the ones left, eventually the sarada line with dilute? Unless sasuke gets hoes? : r/Naruto

Naruto: A complete list of Sasuke Uchiha's eyes

Both Sasuke and Madara's Sharingan awakened/evolved after they broke their bond with their best friends. I love this parallel. : r/Naruto

How did Sasuke and Madara ever exist at the same time since they were both reincarnation of Indra? Did Madara still have his soul? - Quora

Evolution of the Sharingan and Other Eyes: Naruto Shippuuden

Ranking Every Mangekyou Sharingan User in Naruto Strongest to Weakest

Final Awaken of Sasuke? THE GOD EYES All Evolution of Sasuke's Eyes - BiliBili

Question for manga readers, does manga explain how exactly does eternal mongekyo sharingan works? : r/Naruto

Evolution of the Sharingan and Other Eyes: Naruto Shippuuden

Madara Uchiha, Naruto-Fanon Central Wiki

Does evolution of the sharingan + emotional amps make the Uchiha physically stronger? : r/Naruto