Busr binSa'eed said:
"They sent me to Zaid bin Khalid to ask himaboutpassing in front of one who is performing prayer. He told methat theProphet (ﷺ) said: 'Waiting for forty is better than passinginfront of one who is performing prayer.'"(One of the narrators) Sufyan said: "I do not know if he meant forty years, months, days, or hours."
English reference: Vol. 1, Book 5, Hadith 944
Arabic reference: Book 5, Hadith 997