Theorem 2
Tag 0BVO, permanent. Cite it as [Bourbaki, Tag 0BVO].
General Topology, chapter V, § 3. Topological characterization of the groups R and T
A connected group in which there exists a neighbourhood of the identity element homeomorphic to an open interval of is isomorphic to either or .
This is an immediate consequence of the preceding theorem, together with Proposition 7 of § 1, no. 4.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.