Musannaf Ibn Abi Shayba 3:2321

Hushaym narrated to us, he said: Ubaydah narrated to us, from Salim ibn Abi al-Ja’d, who said: The companions of Muhammad used to say that among the signs of the Hour is that *al-madayih* (the arches/niches) are built in the mosques, meaning the *taqat* (arched openings/alcoves).