In Saheeh Ibn Hibbaan and Musnad Ahmad (26/230):
أن نبي الله صلى الله عليه وسلم قال: أربعة يوم القيامة: رجل أصم لا يسمع شيئا، ورجل أحمق، ورجل هرم، ورجل مات في فترة، فأما الأصم فيقول: رب، لقد جاء الإسلام وما أسمع شيئا، وأما الأحمق فيقول: رب، لقد جاء الإسلام والصبيان يحذفوني بالبعر، وأما الهرم فيقول: رب، لقد جاء الإسلام وما أعقل شيئا، وأما الذي مات في الفترة فيقول: رب، ما أتاني لك رسول، فيأخذ مواثيقهم ليطيعنه، فيرسل إليهم أن ادخلوا النار، قال: فوالذي نفس محمد بيده، لو دخلوها لكانت عليهم بردا وسلاما
the Prophet of Allaah SAWS (peace and blessings of Allaah be upon him) said: There are four (who will protest) to Allaah on the Day of Resurrection: the deaf man who never heard anything, the insane man, the very old man, and the man who died during the fatrah (the interval between the time of Eesaa (Jesus, upon whom be peace) and the time of Muhammad SAWS (peace and blessings of Allaah be upon him)). The deaf man will say, O Lord, Islam came but I never heard anything. The insane man will say, O Lord, Islam came but the children ran after me and threw stones at me. The very old man will say, O Lord, Islam came but I did not understand anything. The man who died during the fatrah will say, O Lord, no Messenger from You came to me. He will accept their promises of obedience, then word will be sent to them to enter the Fire. By the One in Whose hand is the soul of Muhammad, if they enter it, it will be cool and safe for them.
Particularly, in this part:
فوالذي نفس محمد بيده، لو دخلوها لكانت عليهم بردا وسلاما
By the One in Whose hand is the soul of Muhammad, if they enter it, it will be cool and safe for them.
What does this mean? Does it mean they will be in Jahannum, but the fire will feel cold and that they won't see Jannah?
Jazakum Allah khayran