﴿ قَالَ رَبِّ ٱجْعَل لِّىٓ ءَايَةًۭ ۚ قَالَ ءَايَتُكَ أَلَّا تُكَلِّمَ ٱلنَّاسَ ثَلَٰثَ لَيَالٍۢ سَوِيًّۭا ﴾

“[Zachariah] prayed: "O my Sustainer! Appoint a sign for me!" Said [the angel]: "Thy sign shall be that for full three nights [and days] thou wilt not speak unto men.”

Please check ayah 19:11 for complete tafsir.