Abul Hasan Ali ibn al-Husayn al-Masoode in his book “Isbat al-Wasiya li Imam Ali ibn Abi Talib” (p 272) narrated that Imam Abu Muhammad al-Askari, 11-th imam of shias said:

Translation:

We group of Awsiya, we don’t reside in the wombs (of our mothers during pregnancy), but we reside in the side (of them)