Usama at 18 was put in charge of the army. "So the people contested his leadership. Rasulullah (ﷺ) said: [He is] one is among the most beloved of people to me after [his father].
Jami` at-Tirmidhi Book 49, Hadith 216
Narrated Ibn 'Umar:

that the Messenger of Allah (ﷺ) sent and army and put Usamah bin Zaid in charge of them. So the people contested his leadership, so the Prophet (ﷺ) said: 'If you contest his leadership, then you did contest the leadership of his father before him. And indeed, by Allah, he was certainly fit for leadership, and he was of the most beloved of people to me, and this one is among the most beloved of people to me after him.'"

حَدَّثَنَا أَحْمَدُ بْنُ الْحَسَنِ، قَالَ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكِ بْنِ أَنَسٍ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم بَعَثَ بَعْثًا وَأَمَّرَ عَلَيْهِمْ أُسَامَةَ بْنَ زَيْدٍ فَطَعَنَ النَّاسُ فِي إِمَارَتِهِ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏ "‏ إِنْ تَطْعَنُوا فِي إِمَارَتِهِ فَقَدْ كُنْتُمْ تَطْعَنُونَ فِي إِمْرَةِ أَبِيهِ مِنْ قَبْلُ وَايْمُ اللَّهِ إِنْ كَانَ لَخَلِيقًا لِلإِمَارَةِ وَإِنْ كَانَ مِنْ أَحَبِّ النَّاسِ إِلَىَّ وَإِنَّ هَذَا مِنْ أَحَبِّ النَّاسِ إِلَىَّ بَعْدَهُ ‏"‏ ‏. هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ ‏.
Reference  : Jami` at-Tirmidhi Book 49, Hadith 216
In-book reference  : Vol. 1, Book 46, Hadith 3816