Titus 1:9 holding fast the faithful word which is in accordance with the teaching, so that he will be able both to exhort in sound doctrine and to refute those who contradict.
Please show where "the teaching" included the assumption of Mary and the requirement to believe it.
“Please show where “the teaching” included the assumption of Mary and the requirement to believe it.”
Notice that it doesn’t say that the teaching must be in scripture explicitly? Notice how it says in “accordance” with rather than “according to sola scriptura”? Thus, here is the teaching you asked for: http://w2.vatican.va/content/pius-xii/en/apost_constitutions/documents/hf_p-xii_apc_19501101_munificentissimus-deus.html
The typical anti-Catholic would now claim he actually wanted something according to sola scriptura instead. What will you do?