TABARANI 15373:
from ʿImrān b. Ḥuṣayn —
[Machine] From the prophet ﷺ , he said to him or someone else: "Did you keep the secret of this month?" He said, "No." He said, "If the people break their fast or you break your fast, then fast for two days."
الطبراني ١٥٣٧٣:
عن عمران بن حصين —
عَنِ النَّبِيِّ ﷺ قَالَ لَهُ أَوْ لِغَيْرِهِ «أَصُمْتَ سِرَارَ هَذَا الشَّهْرِ؟» قَالَ لَا قَالَ «إِذَا أَفْطَرَ النَّاسُ أَوْ أَفْطَرْتَ فَصُمْ يَوْمَيْنِ»