We know from the sayings of Prophet Muhammad (peace be upon him) that sometime after 120 days after conception, the soul and the flesh are brought together. He (peace be upon him) says:

“Verily the creation of each one of you is brought together in his mother’s belly for forty days in the form of seed, then he is a clot of blood for a like period, then a morsel of flesh for a like period, then there is sent to him the angel who blows the breath of life into him…” (Abdullah bin Masud in Bukhari and Muslim, Riyad-us-Saliheen # 396)