|You could do it with a User Defined Function (UDF)|
Place this code in a Standard Module and enter =MinBySheet() in any cell (except A2 of course).
The UDF starts by assuming that Sheet1!A2 contains the lowest value. It then compares Sheet2!A2 to Sheet1!A2 and if it's lower, it reassigns the nxtShtName and nxtVal variables to the name of Sheet2 and the value in Sheet2!A2.
It then does the same thing for all sheets, updating the variables when it finds a lower value. Once it goes through all the sheets, it returns whatever Sheet.Name and A2 value that are currently stored in those variables.
Dim nxtVal As Variant
Dim nxtShtName As String
Dim nxtSht As Integer
nxtVal = Sheets(1).Range("A2")
nxtShtName = Sheets(1).Name
For nxtSht = 2 To Sheets.Count
If Sheets(nxtSht).Range("A2") < nxtVal Then
nxtVal = Sheets(nxtSht).Range("A2")
nxtShtName = Sheets(nxtSht).Name
MinBySheet = nxtShtName & "!A2 = " & nxtVal