What’s proof for hadd on an unmarried pregnant woman in the Maliki madhab?

With All due respect, the ruling in the Maliki madhab with regards to hadd on an unmarried pregnant woman (her pregnancy being proof)seems very unjust if she was truly raped. How could such an individual provide ample evidence for being raped? It would be difficult, especially in the past. The other 3 madhahib have proof from the Sunnah & accept verbal proof even, for the Malikiyya, I’ve come a cross a statement of Imam Maalik & so on(No Hadith reference). What proof do they use for this ruling? The statement of Imām Mālik seems very harsh and inconsiderate considering how serious the hadd is. In the Sunnah it’s clear that postponing the punishment for Zina is practiced, and it doesn’t seem so from the statement of Mālik & co.