Musannaf Ibn Abi Shayba 1:2067

Hussain bin Ali narrated to us, from Za'idah, from Mansur, who said: I said to Ibrahim, "A man forgets to perform *istinshaq* (sniffing water into the nose), then remembers during the prayer that he forgot it." Ibrahim said, "He should proceed with his prayer." Mansur said, "And *madmadah* (rinsing the mouth) is the same as that."