In one narration the wording is: "They are allies of one another in this world and the Hereafter."
Imam Ahmad and Imam al-Tabarani recorded it with various chains. One of al-Tabarani's chains has narrators who are the narrators of the Sahih; he transmitted its chain well, for he narrated it from al-A'mash, from Musa bin Abdullah bin Yazid, from Abd al-Rahman bin Hilal al-Absi, from Sayyiduna Jarir (may Allah be pleased with him), and this is correct. In the "Musnad", however, its chain is that it is reported from Musa bin Abdullah bin Hilal al-Absi from Sayyiduna Jarir (may Allah be pleased with him); and Musa bin Abdullah did not hear from Sayyiduna Jarir (may Allah be pleased with him), and he is not Musa bin Abdullah bin Hilal al-Absi. And Allah knows best.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب المناقب / 16375