Zirr b. Hubaish said:I questioned Ubayy b. Ka'b about a statement by his brother [not actual brother] Ibn Mas'ud to the effect that anyone who gets up for prayer every night in the year will hit upon lailat al-qadr, and he replied,“God have mercy on him! He meant that people should not content themselves [with that might alone] . He knew that it was in Ramadan among the last ten nights and that it was the twenty-seventh.”He then swore without any reservation that it was the twenty-seventh, and when I asked,“On what ground do you state that, Abul Mundhir? [Ubayy's kunya] ”he replied,“By the indication (or sign)* of which God’s messenger informed us, viz. that the sun rises on that day without rays.”*An alternative, the transmitter not being sure which word was used. *An alternative, the transmitter not being sure which word was used. Muslim transmitted it.