Hadith: 12000 muslims will not be defeated - sahih?

Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
167. Chapter: On the Recommendation to have company on a journey and
the travellers should appoint someone as their amir whom they will
obey.
961. Ibn 'Abbas reported that the Prophet, may Allah bless him and
grant him peace, said, "The best [number] of companions is four, and
the best of expeditions is 400 and the best of armies is 4000.12,000
Muslims will not be defeated for lack of numbers."
- [Abu Dawud and at-Tirmidhi]
Assalamu alaykom,
A. Can someone confirm the soundness of this hadith?
B. Is there a website where one can enter an hadith or part of an
hadith into a seach engine& obtain its soundness?

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