Sayyiduna Wa'il bin Hujr (may Allah be pleased with him) says: I heard that when the Noble Prophet (peace and blessings be upon him) recited {وَلَاالضَّالِّیْنَ}, he said Ameen and would prolong his voice with it (Ameen).
Hadith Referenceالفتح الربانی / أبواب صفة الصلاة / 1595
Benefits: … The wording of the narration in Sunan al-Bayhaqi is: "yarfa‘u biha sawtahu" (he would raise his voice with it). That is, the Prophet sallallahu alayhi wa sallam would raise his voice when saying "Ameen." There is no contradiction between the two narrations; rather, the meaning is that when saying "Ameen," he would both prolong his voice and raise it. (Abdullah Rafiq)