See Instruction on Priesthood, between ca. 1 Mar. and ca. 4 May 1835 [D&C 107:95–96]. The number 144,000 may have been an allusion to Revelation 7:4. (See also Answers to Questions, between ca. 4 and ca. 20 Mar. 1832 [D&C 77:11].)
According to the minutes of an October 1831 conference, JS stated at that time that “the Lord held the Church bound to provide for the families of the absent Elders while proclaiming the Gospel.” (Minutes, 25–26 Oct. 1831; see also Revelation, 25 Jan. 1832–B [D&C 75:24].)