I Samuel 1:22

When [the boy] will be weaned. At the end of twenty-two (other versions, twenty-four) months, for that is the period for a child to nurse.

And shall remain there forever. Forever in the Levitic sense, i.e., fifty years as it is said, "from the age of fifty he shall retire from the work force." Figuring as follows, we determine that Shmuel's lifetime was fifty-two years: Eili judged Yisroel for forty years. On the day of Chana's prayer he was appointed judge. By subtracting the year in which Chana conceived Shmuel, there remain thirty-nine years. Shmuel governed Yisroel from the time of Eili's death for thirteen years, as follows: On the day of Eili's death, the Ark was captured, and it remained in the land of the Philistines for seven months. From there, it was brought to and remained in Kiryas Yearim until Dovid brought it up after he had reigned seven years in Chevron over Yehudah, and all of Yisroel had accepted him as their king. And it is written, "From the day the Ark came to rest in Kiryas Yearim, there ensued many days, and they became twenty years." Subtracting from them seven years which Dovid reigned in Chevron discloses that from the time the Ark was captured until Shaul's death, were thirteen years and seven months; and Shmuel died four months before Shaul.

Until the boy will be weaned: Until the end of his nursing, and that is the twenty-four months that an infant nurses. And even though they were obligated to bring him [to Shiloh] on account of, "every male shall appear" (Exodus 23:17) - our Rabbis, may their memory be blessed, said it was because she saw that he was pampered and weak, so she was concerned lest he fall sick because of the travel.

And he shall abide there forever: As she had vowed about him, "and I will give him to the Lord" (I Samuel 1:11). And the explantion of, "forever," is all the days of his life. And our Rabbis, may their memory be blessed, expounded - the forever of the Levites, since they would serve fifty years, as it is written (Numbers 8:25), "From the age of fifty he shall retire from the work force." And they said that all the days of Shmuel were only fifty-two years: As Channah had already said, "and I will give him to the Lord all the days of his life." And she said, "And he shall abide there forever" - and that is the forever of the Levites, which is fifty years. And from when he came to the House of the Lord until the day of his death was fifty years. And the [other] two years were when he nursed, as it is written, "until the boy will be weaned." And it is the way of a child to nurse twenty-four months. There you have fifty-two years.