Tosefta על ברכות 5:2

[In] a place where it is customary to say Birkat Aveilim (Blessing of the Mourners), [if the custom is to say] three [Berachot (blessings)], [then] they say three [Berachot]. [If the custom is to say] two [Berachot], [then] they say two [Berachot]. [If the custom is to say] one [Beracha], [then] they say one [Beracha]. [In] a place where it is customary to say Birkat Aveilim (Blessing of the Mourners), [if the custom is to say] three [Berachot] including the first one [on the subject of] Techiyat Hametim (Resurrection of the Dead) and he seals it off [by saying Baruch Ata Hashem] Mechayeh Hametim (Blessed are You Hashem Who resurrects the dead). The second [Beracha is on the subject of] Tanchumei Aveilim (Consolation of the Mourners), and he seals it off [by saying Baruch Ata Hashem] Menachem Amo Veiro (Blessed are You Hashem who consoles His nation and His city). The third [Beracha is said on the subject of] Gemilut Chasadim (Deeds of Kindness), and he does not seal it off.